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Ohio River
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Ohio River
The widest point on the Ohio River is just north of downtown Louisville, where it is one mile (1.6 km) wide
Country
United States
States
Pennsylvania, Ohio, West Virginia, Kentucky, Indiana, Illinois
Tributaries
- left Little Kanawha River, Kanawha River, Guyandotte River, Big Sandy River, Little Sandy River, Licking River, Kentucky River, Salt River, Green River, Cumberland River, Tennessee River
- right Beaver River, Little Muskingum River, Muskingum River, Little Hocking River, Hocking River, Shade River, Scioto River, Little Miami River, Great Miami River, Wabash River
Cities
Pittsburgh, PA, East Liverpool, OH, Wheeling, WV, Parkersburg, WV, Huntington, WV, Ashland, KY, Cincinnati, OH, Louisville, KY, Owensboro, KY, Evansville, IN, Henderson, KY, Paducah, KY, Cairo, IL
Source
Allegheny River
- location Allegany Township, Potter County, Pennsylvania
- elevation 2,240 ft (683 m)
- coordinates 41°52′22″N 77°52′30″W / 41.87278°N 77.87500°W / 41.87278; -77.87500
Secondary source
Monongahela River
- location Fairmont, West Virginia
- elevation 880 ft (268 m)
- coordinates 39°27′53″N 80°09′13″W / 39.46472°N 80.15361°W / 39.46472; -80.15361
Source confluence
- location Pittsburgh, Pennsylvania
- elevation 730 ft (223 m)
- coordinates 40°26′32″N 80°00′52″W / 40.44222°N 80.01444°W / 40.44222; -80.01444
Mouth
Mississippi River
- location at Cairo, Illinois / Ballard County, Kentucky
- elevation 290 ft (88 m)
- coordinates 36°59′12″N 89°07′50″W / 36.98667°N 89.13056°W / 36.98667; -89.13056Coordinates: 36°59′12″N 89°07′50″W / 36.98667°N 89.13056°W / 36.98667; -89.13056
Length
981 mi (1,579 km)
Basin
189,422 sq mi (490,601 km2)
Discharge
for Cairo, Illinois
- average 281,000 cu ft/s (7,957 m3/s) (1951–80)[1]
- max 1,850,000 cu ft/s (52,386 m3/s)
Ohio River basin
The Ohio River, which streams westward from Pittsburgh, Pennsylvania, to Cairo, Illinois, is the largest tributary, by volume, of the Mississippi River in the United States. At the confluence, the Ohio is considerably bigger than the Mississippi (Ohio at Cairo: 281,500 cu ft/s (7,960 m3/s);[2] Mississippi at Thebes: 208,200 cu ft/s (5,897 m3/s)[3]) and, thus, is hydrologically the main stream of the whole river system.
The 981-mile (1,579 km) river flows through or along the border of six states, and its drainage basin includes parts of 15 states. Through its largest tributary, the Tennessee River, the basin includes many of the states of the southeastern U.S. It is the source of drinking water for three million people.[4]
It is named in Iroquoian or Seneca: Ohi:yó, lit. "Good River"[5] or Shawnee: Pelewathiipi and Spelewathiipi.[6] The river had great significance in the history of the Native Americans, as numerous civilizations formed along its valley. For thousands of years, Native Americans used the river as a major transportation and trading route. Its waters connected communities. In the five centuries before European conquest, the Mississippian culture built numerous regional chiefdoms and major earthwork mounds in the Ohio Valley, such as Angel Mounds near Evansville, Indiana, as well as in the Mississippi Valley and the Southeast. The Osage, Omaha, Ponca and Kaw lived in the Ohio Valley, but under pressure from the Iroquois to the northeast, migrated west of the Mississippi River to Missouri, Arkansas and Oklahoma in the 17th century.
In 1669, René-Robert Cavelier, Sieur de La Salle led a French expedition to the Ohio River, becoming the first Europeans to see it. After European-American settlement, the river served as a border between present-day Kentucky and Indian Territories. It was a primary transportation route for pioneers during the westward expansion of the early U.S. In his Notes on the State of Virginia published in 1781–82, Thomas Jefferson stated: "The Ohio is the most beautiful river on earth. Its current gentle, waters clear, and bosom smooth and unbroken by rocks and rapids, a single instance only excepted."[7]
During the 19th century, the river was the southern boundary of the Northwest Territory. It is sometimes considered as the western extension of the Mason–Dixon Line that divided Pennsylvania from Maryland, and thus part of the border between free and slave territory, and between the Northern and Southern United States or Upper South. Where the river was narrow, it was the way to freedom for thousands of slaves escaping to the North, many helped by free blacks and whites of the Underground Railroad resistance movement.
The Ohio River is a climatic transition area, as its water runs along the periphery of the humid subtropical and humid continental climate areas. It is inhabited by fauna and flora of both climates. In winter, it regularly freezes over at Pittsburgh but rarely farther south toward Cincinnati and Louisville. At Paducah, Kentucky, in the south, near the Ohio's confluence with the Mississippi, it is ice-free year-round. Paducah was founded there because it is the northernmost ice-free reach of the Ohio.
Contents
[hide]
1 Gallery
2 Geography and hydrography
2.1 Drainage basin
3 Geology
3.1 Upper Ohio River
3.2 Middle Ohio River
4 History
5 Pollution
6 River depth
7 Cities and towns along the river
8 See also
9 Notes
10 References
11 Further reading
12 External links
Gallery[edit]
The Allegheny River, left, and Monongahela River join to form the Ohio River at Pittsburgh, Pennsylvania, the largest metropolitan area on the river.
Built between 1849 and 1851, the Wheeling Suspension Bridge was the first bridge across the river.
Louisville, Kentucky, The deepest point of the Ohio River is a scour hole just below Cannelton locks and dam (river mile 720.7). The widest point of the river is at the confluence of the Ohio and the Mississippi rivers.
A barge hauls coal in the Louisville and Portland Canal, the only artificial portion of the Ohio River.
The Tall Stacks festival celebrates the riverboats of Cincinnati, Ohio, every three or four years.
Geography and hydrography[edit]
Natural-color satellite image of the Wabash-Ohio confluence.
The Ohio River is formed by the confluence of the Allegheny and Monongahela rivers at Point State Park in Pittsburgh, Pennsylvania. From there, it flows northwest through Allegheny and Beaver counties, before making an abrupt turn to the south-southwest at the West Virginia–Ohio–Pennsylvania triple-state line (near East Liverpool, Ohio; Chester, West Virginia; and Midland, Pennsylvania). From there, it forms the border between West Virginia and Ohio, upstream of Wheeling, West Virginia.
The river then follows a roughly southwest and then west-northwest course until Cincinnati, before bending to a west-southwest course for most of its length. The course forms the northern borders of West Virginia and Kentucky; and the southern borders of Ohio, Indiana and Illinois, until it joins the Mississippi River near the city of Cairo, Illinois.
Major tributaries of the river, indicated by the location of the mouths, include:
Allegheny River – Pittsburgh, Pennsylvania
Monongahela River – Pittsburgh, Pennsylvania
Saw Mill Run – Pittsburgh, Pennsylvania
Chartiers Creek – Pittsburgh, Pennsylvania
Montour Run – Coraopolis, Pennsylvania
Beaver River – Rochester, Pennsylvania
Breezewood Creek – Beaver, Pennsylvania
Raccoon Creek – Center Township
Little Beaver Creek – East Liverpool, Ohio
Wheeling Creek – Wheeling, West Virginia
Middle Island Creek – St. Marys, West Virginia
Little Muskingum River – Ohio
Duck Creek – Marietta, Ohio
Muskingum River – Marietta, Ohio
Little Kanawha River – Parkersburg, West Virginia
Hocking River – Hockingport, Ohio
Kanawha River – Point Pleasant, West Virginia
Guyandotte River – Huntington, West Virginia
Big Sandy River – Kentucky-West Virginia border
Little Sandy River – Greenup, Kentucky
Little Scioto River – Sciotoville, Ohio
Scioto River – Portsmouth, Ohio
Kinniconick Creek – Vanceburg, Kentucky
Little Miami River – Cincinnati, Ohio
Licking River – Newport-Covington, Kentucky
Mill Creek – Cincinnati, Ohio
Great Miami River – Ohio-Indiana border
Salt River – West Point, Kentucky
Kentucky River – Carrollton, Kentucky
Green River – near Henderson, Kentucky
Wabash River – Indiana-Illinois-Kentucky border
Saline River – Illinois
Cumberland River – Smithland, Kentucky
Tennessee River – Paducah, Kentucky
Cache River – Illinois
Drainage basin[edit]
The Ohio's drainage basin covers 189,422 square miles (490,600 km2), encompassing the easternmost regions of the Mississippi Basin. The Ohio drains parts of 15 states in four regions.
Northeast
New York: a small area of the southern border along the headwaters of the Allegheny.
Pennsylvania: a corridor from the southwestern corner to north central border.
Mid-Atlantic/Upper South
Maryland: a small corridor along the Youghiogheny River on the western border.
West Virginia: all but the Eastern Panhandle.
Kentucky: all but a small part in the extreme west drained directly by the Mississippi.
Tennessee: all but a small part in the extreme west drained directly by the Mississippi, and a very small area in the southeastern corner which is drained by the Conasauga River.
Virginia: most of southwest Virginia.
North Carolina: the western quarter.
Midwest
Ohio: the southern two-thirds
Indiana: all but the northern area.
Illinois: the southeast quarter.
Deep South
Georgia: the far northwest corner.
Alabama: the northern portion.
Mississippi: the northeast corner.
South Carolina: less than 1 square mile in the northwest.
Geology[edit]
Glacial Lake Ohio
From a geological standpoint, the Ohio River is young. The river formed on a piecemeal basis beginning between 2.5 and 3 million years ago. The earliest ice ages occurred at this time and dammed portions of north-flowing rivers. The Teays River was the largest of these rivers. The modern Ohio River flows within segments of the ancient Teays. The ancient rivers were rearranged or consumed by glaciers and lakes.
Upper Ohio River[edit]
The upper Ohio River formed when one of the glacial lakes overflowed into a south-flowing tributary of the Teays River. Prior to that event, the north-flowing Steubenville River (no longer in existence) ended between New Martinsville and Paden City, West Virginia. Likewise, the south-flowing Marietta River (no longer in existence) ended between the present-day cities. The overflowing lake carved through the separating hill and connected the rivers.
The resulting floodwaters enlarged the small Marietta valley to a size more typical of a large river. The new large river subsequently drained glacial lakes and melting glaciers at the end of the Ice Age. The valley grew during and following the ice age.
Many small rivers were altered or abandoned after the upper Ohio River formed. Valleys of some abandoned rivers can still be seen on satellite and aerial images of the hills of Ohio and West Virginia between Marietta, Ohio, and Huntington, West Virginia. As testimony to the major changes that occurred, such valleys are found on hilltops.[clarification needed]
Middle Ohio River[edit]
The middle Ohio River formed in a manner similar to formation of the upper Ohio River. A north-flowing river was temporarily dammed southwest of present-day Louisville, creating a large lake until the dam burst. A new route was carved to the Mississippi. Eventually the upper and middle sections combined to form what is essentially the modern Ohio River.
History[edit]
Steamboat "Morning Star", a Louisville and Evansville mail packet, in 1858.
Pre-Columbian inhabitants of eastern North America considered the Ohio part of a single river continuing on through the lower Mississippi. The river's name comes from the Seneca (Iroquoian) Ohiːyo', a proper name derived from ohiːyoːh, meaning "good river".[8] The combined Allegheny-Ohio river is 1,310 miles (2,110 km) long and carries the largest volume of water of any tributary of the Mississippi. The Indians and early explorers and settlers of the region also often considered the Allegheny to be part of the Ohio. The forks (the confluence of the Allegheny and Monongahela rivers at what is now Pittsburgh) was considered a strategic military location.
French fur traders operated in the area, and France built forts along the Allegheny River. In 1669, René-Robert Cavelier, Sieur de La Salle, led an expedition of French traders who became the first Europeans to see the river. He traveled from Canada and entered the headwaters of the Ohio, traveling as far as the Falls of Ohio at present-day Louisville before turning back. He returned to explore the river again in other expeditions. An Italian cartographer traveling with him created the first map of the Ohio River. La Salle claimed the Ohio Valley for France.
In 1749, Great Britain established the Ohio Company to settle and trade in the area. Exploration of the territory and trade with the Indians in the region near the Forks by British colonials from Pennsylvania and Virginia – both of which claimed the territory – led to conflict with the French. In 1763, following the Seven Years' War, France ceded the area to Britain.[9]
The 1768 Treaty of Fort Stanwix opened Kentucky to colonial settlement and established the Ohio River as a southern boundary for American Indian territory.[10] In 1774, the Quebec Act restored the land east of the Mississippi River and north of the Ohio River to Quebec, in effect making the Ohio the southern boundary of Canada. This appeased the Canadien British subjects but angered the Thirteen Colonies. Lord Dunmore's War south of the Ohio river also contributed to giving the land north to Quebec to stop further encroachment of the British colonials on native land. During the American Revolution, in 1776 the British military engineer John Montrésor created a map of the river showing the strategic location of Fort Pitt, including specific navigational information about the Ohio River's rapids and tributaries in that area.[11] However, the Treaty of Paris (1783) gave the entire Ohio Valley to the United States.
The economic connection of the Ohio Country to the East was significantly increased in 1818 when the National Road being built westward from Cumberland, Maryland reached Wheeling, Virginia (now West Virginia), providing an easier overland connection from the Potomac River to the Ohio River.[12]
Louisville was founded at the only major natural navigational barrier on the river, the Falls of the Ohio. The Falls were a series of rapids where the river dropped 26 feet (7.9 m) in a stretch of about 2 miles (3.2 km). In this area, the river flowed over hard, fossil-rich beds of limestone. The first locks on the river – the Louisville and Portland Canal – were built to circumnavigate the falls between 1825 and 1830. Fears that Louisville's transshipment industry would collapse proved ill-founded: the increasing size of steamships and barges on the river meant that the outdated locks could only service the smallest vessels until well after the Civil War. The U.S. Army Corps of Engineers improvements were expanded again in the 1960s, forming the present-day McAlpine Locks and Dam.
Because the Ohio River flowed westward, it became a convenient means of westward movement by pioneers traveling from western Pennsylvania. After reaching the mouth of the Ohio, settlers would travel north on the Mississippi River to St. Louis, Missouri. There, some continued on up the Missouri River, some up the Mississippi, and some further west over land routes. In the early 19th century, river pirates such as Samuel Mason, operating out of Cave-In-Rock, Illinois, waylaid travelers on their way down the river. They killed travelers, stealing their goods and scuttling their boats. The folktales about Mike Fink recall the keelboats used for commerce in the early days of European settlement. The Ohio River boatmen were the inspiration for performer Dan Emmett, who in 1843 wrote the song "The Boatman's Dance".
Trading boats and ships traveled south on the Mississippi to New Orleans, and sometimes beyond to the Gulf of Mexico and other ports in the Americas and Europe. This provided a much-needed export route for goods from the west, since the trek east over the Appalachian Mountains was long and arduous. The need for access to the port of New Orleans by settlers in the Ohio Valley led to the Louisiana Purchase in 1803.
Because the river is the southern border of Ohio, Indiana, and Illinois, it was part of the border between free states and slave states in the years before the American Civil War. The expression "sold down the river" originated as a lament of Upper South slaves, especially from Kentucky, who were shipped via the Ohio and Mississippi to cotton and sugar plantations in the Deep South.[13][14] Before and during the Civil War, the Ohio River was called the "River Jordan" by slaves crossing it to escape to freedom in the North via the Underground Railroad.[15] More escaping slaves, estimated in the thousands, made their perilous journey north to freedom across the Ohio River than anywhere else across the north-south frontier. Harriet Beecher Stowe's Uncle Tom's Cabin, the bestselling novel that fueled abolitionist work, was the best known of the anti-slavery novels that portrayed such escapes across the Ohio. The times have been expressed by 20th-century novelists as well, such as the Nobel Prize-winning Toni Morrison, whose novel Beloved was adapted as a film of the same name. She also composed the libretto for the opera Margaret Garner (2005), based on the life and trial of an enslaved woman who escaped with her family across the river.
The Ohio River is considered to separate Midwestern Great Lakes states from the Upper South states, which were historically border states in the Civil War.
The colonial charter for Virginia defined its territory as extending to the north shore of the Ohio, so that the riverbed was "owned" by Virginia. Where the river serves as a boundary between states today, Congress designated the entire river to belong to the states on the east and south, i.e., West Virginia and Kentucky at the time of admission to the Union, that were divided from Virginia. Thus Wheeling Island, the largest inhabited island in the Ohio River, belongs to West Virginia, although it is closer to the Ohio shore than to the West Virginia shore. Kentucky brought suit against Indiana in the early 1980s because of the building of the Marble Hill nuclear power plant in Indiana, which would have discharged its waste water into the river.
The U.S. Supreme Court held that Kentucky's jurisdiction (and, implicitly, that of West Virginia) extended only to the low-water mark of 1793 (important because the river has been extensively dammed for navigation, so that the present river bank is north of the old low-water mark.) Similarly, in the 1990s, Kentucky challenged Illinois' right to collect taxes on a riverboat casino docked in Metropolis, citing its own control of the entire river. A private casino riverboat that docked in Evansville, Indiana, on the Ohio River opened about the same time. Although such boats cruised on the Ohio River in an oval pattern up and down, the state of Kentucky soon protested. Other states had to limit their cruises to going forwards, then reversing and going backwards on the Indiana shore only. Since 2002, Indiana has allowed its riverboat casinos to be permanently docked.
In the early 1980s, the Falls of the Ohio National Wildlife Conservation Area was established at Clarksville, Indiana.
The confluence of the Mississippi and Ohio rivers is at Cairo, Illinois.
Carl D. Perkins Bridge in Portsmouth, Ohio with Ohio River and Scioto River tributary on right.
Silver Bridge in Point Pleasant, West Virginia which collapsed into the Ohio River on December 15, 1967, killing 46 persons.
Mouth of the Ohio, as it feeds into the Mississippi.
Cave-in-rock, view on the Ohio (circa 1832, Cave-In-Rock, Illinois): aquatint by Karl Bodmer from the book Maximilian, Prince of Wied's Travels in the Interior of North America, during the years 1832–1834
Pollution[edit]
The Ohio River as a whole is ranked as the most polluted river in the US based on 2009 and 2010 data although the more industrial and regional Ohio tributary, Monongahela River, ranked behind 16 other American rivers for pollution at number 17.[16]
The Ohio River was polluted with hundreds of thousands of pounds of PFOA by DuPont chemical company, from an outflow pipe, for several decades beginning in the 1950s.[17]
River depth[edit]
Lawrenceburg, Indiana, is one of many towns that use the Ohio as a shipping avenue.
The Ohio River is a naturally shallow river that was artificially deepened by a series of dams. The natural depth of the river varied from about 3 to 20 feet (0.91 to 6.10 m). The dams raise the water level and have turned the river largely into a series of reservoirs, eliminating shallow stretches and allowing for commercial navigation. From its origin to Cincinnati, the average depth is approximately 15 feet (5 m). The largest immediate drop in water level is below the McAlpine Locks and Dam at the Falls of the Ohio at Louisville, Kentucky, where flood stage is reached when the water reaches 23 feet (7 m) on the lower gauge. However, the river's deepest point is 168 feet (51 m) on the western side of Louisville, Kentucky. From Louisville, the river loses depth very gradually until its confluence with the Mississippi at Cairo, Illinois, where it has an approximate depth of 19 feet (6 m).
Water levels for the Ohio River from Smithland Lock and Dam upstream to Pittsburgh are predicted daily by the National Oceanic and Atmospheric Administration's Ohio River Forecast Center.[18] The water depth predictions are relative to each local flood plain based upon predicted rainfall in the Ohio River basin in five reports as follows:
Pittsburgh, Pennsylvania, to Hannibal Locks and Dam, Ohio (including the Allegheny and Monongahela rivers)
Willow Island Locks and Dam, Ohio, to Greenup Lock and Dam, Kentucky (including the Kanawha River)
Portsmouth, Ohio, to Markland Locks and Dam, Kentucky
McAlpine Locks and Dam, Kentucky, to Cannelton Locks and Dam, Indiana
Newburgh Lock and Dam, Indiana, to Golconda, Illinois
The water levels for the Ohio River from Smithland Lock and Dam to Cairo, Illinois, are predicted by the National Oceanic and Atmospheric Administration's Lower Mississippi River Forecast Center.[19]
Smithland Lock and Dam, Illinois, to Cairo, Illinois
Panorama of the Ohio at its widest point, just west of downtown Louisville, Kentucky
Cities and towns along the river[edit]
Metro Area
Population
Pittsburgh 2.4 million
Cincinnati 2.2 million
Louisville 1.4 million
Huntington-Ashland 365,419
Evansville 358,000
Parkersburg 160,000
Wheeling 145,000
Weirton-Steubenville 132,000
Owensboro 112,000
Cities along the Ohio River include:
Pennsylvania
Pittsburgh
Sewickley
McKees Rocks
Coraopolis
South Heights
Ambridge
Aliquippa
Rochester
Monaca
Beaver
Shippingport
Midland
Freedom
Rochester
Conway
Neville Island
Baden
Bellevue
Edgeworth
Leetsdale
Ohio
East Liverpool
Steubenville
Martins Ferry
Bellaire
Marietta
Belpre
Pomeroy
Gallipolis
Ironton
Portsmouth
New Boston
Manchester
Aberdeen
Ripley
New Richmond
Cincinnati
West Virginia
Chester
Weirton
Wheeling
Moundsville
New Martinsville
Paden City
Sistersville
St. Marys
Parkersburg
Ravenswood
Point Pleasant
Huntington
Kenova
Kentucky
Big Bone
Rabbit Hash
Constance
Hamilton
Petersburg
Belleview
Henderson
Uniontown
Ashland
Vanceburg
Maysville
Augusta
Fort Thomas
Newport
Covington
Ludlow
Louisville
Hawesville
Lewisport
Owensboro
Paducah
Smithland
Warsaw
Ghent
Carrollton
Brandenburg
Bellevue
Dayton
Concord
Indiana
Lawrenceburg
Aurora
Rising Sun
Vevay
Madison
Jeffersonville
Clarksville
New Albany
Cannelton
Tell City
Troy
Rockport
Newburgh
Evansville
Mount Vernon
Illinois
Old Shawneetown
Cave-In-Rock
Elizabethtown
Rosiclare
Golconda
Brookport
Metropolis
Mound City
Cairo
See also[edit]
Geography of the United States
Islands of the Midwest
List of crossings of the Ohio River
List of islands of West Virginia (including islands on Ohio River)
List of locks and dams of the Ohio River
List of rivers of Indiana
List of rivers of Kentucky
List of rivers of Ohio
List of rivers of Pennsylvania
List of variant names of the Ohio River
Ohio and Erie Canal
Ohio River Bridges Project
Ohio River flood of 1937
Watersheds of Illinois
List of longest rivers of the United States (by main stem)
Ohio River Valley AVA
Ohio Valley in Kentucky
Ohio River Trail
Ohio River Water Trail
Notes[edit]
Jump up ^ Leeden, Frits van der; Troise, Fred L.; Todd, David Keith (1990). The Water Encyclopedia (2nd ed.). Chelsea, Mich.: Lewis Publishers. p. 126. ISBN 0-87371-120-3.
Jump up ^ Frits van der Leeden, Fred L. Troise, David Keith Todd: The Water Encyclopedia, 2nd edition, p. 126, Chelsea, Mich. (Lewis Publishers), 1990, ISBN 0-87371-120-3 (long term mean discharge)
Jump up ^ USGS stream gage 07022000 Mississippi River at Thebes, IL (long term mean discharge)
Jump up ^ "Ohio River Facts".
Jump up ^ Bright, William (2004). Native American Placenames of the United States. University of Oklahoma Press. p. 344. ISBN 9780806135984. OHIO River \ō hī′ ō\. From Seneca (Iroquoian) ohi:yo’, a proper name derived from ohi:yo:h 'good river'.
Jump up ^ "Shawnees Webpage". Shawnee's Reservation. 1997. Retrieved April 26, 2013.
Jump up ^ Jefferson, Thomas, 1743–1826. Notes on the State of Virginia Archived August 29, 2013, at the Wayback Machine.; the single instance refers to the former rapids near Louisville.
Jump up ^ Bright, William (2004). Native American placenames of the United States. University of Oklahoma Press. p. 344. ISBN 978-0-8061-3598-4. Retrieved April 11, 2011.
Jump up ^ "History of Seneca County: Containing a Detailed Narrative of the Principal Events That Have Occurred Since Its First Settlement Down to the Present Time; a History of the Indians That Formerly Resided Within Its Limits; Geographical Descriptions, Early Customs, Biographical Sketches, &c., &c., With an Introd., Containing a Brief History of the State, From the Discovery of the Mississippi River Down to the Year 1817, to the Whole of Which Is Added an Appendix, Containing Tabular Views, &c". Mocavo.
Jump up ^ * Taylor, Alan (2006). The Divided Ground: Indians, Settlers, and the Northern Borderland of the American Revolution. New York: Alfred A. Knopf. p. 44, see map on 39. ISBN 0-679-45471-3.
Jump up ^ Montrésor, John (1776). "Map of the Ohio River from Fort Pitt". World Digital Library. Pennsylvania. Retrieved July 1, 2013.
Jump up ^ Fowler, Thaddeus Mortimer (1906). "Bird's Eye View of Cumberland, Maryland 1906". World Digital Library. Retrieved July 22, 2013.
Jump up ^ mginter. "KET's Underground Railroad – Behind the Scenes – Guy Mendes".
Jump up ^ "Put in Master's Pocket: Interstate Slave Trading and the Black Appalachian Diaspora" Archived August 18, 2007, at the Wayback Machine.
Jump up ^ mginter. "KET's Underground Railroad – Community Research".
Jump up ^ "Report: Ohio River most polluted in U.S". Pittsburgh Business Times. March 23, 2012. Retrieved April 24, 2012.
Jump up ^ Rich, Nathaniel (January 6, 2016). "The Lawyer Who Became DuPont's Worst Nightmare". New York Times.
Jump up ^ "Ohio RFC". US Department of Commerce, NOAA, National Weather Service. Retrieved March 10, 2017.
Jump up ^ "Lower Mississippi RFC". US Department of Commerce, NOAA, National Weather Service. Retrieved March 10, 2017.
References[edit]
Hay, Jerry (2010). Ohio River Guidebook, 1st Edition
Further reading[edit]
Dunn, J. P. (December 1912). "Names of the Ohio River". The Indiana Quarterly Magazine of History. 8 (4): 166–70. doi:10.2307/27785389 (inactive 2017-03-10). JSTOR 27785389.
External links[edit]
Wikimedia Commons has media related to Ohio River.
Ohio River Flows and Forecasts
U.S. Geological Survey: PA stream gauging stations
Ohio River Forecast Center, which issues official river forecasts for the Ohio River and its tributaries from Smithland Lock and Dam upstream
Lower Mississippi River Forecast Center, which issues official river forecasts for the Ohio River and its tributaries downstream of Smithland Lock and Dam
Texts on Wikisource:
"Ohio River". Encyclopædia Britannica. 20 (11th ed.). 1911.
"Ohio River". The American Cyclopædia. 1879.
"Ohio River". New International Encyclopedia. 1905.
"Ohio, a river of the United States". The New Student's Reference Work. 1914.
"Ohio, a river of the United States". Collier's New Encyclopedia. 1921.
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Dark matter halo
From Wikipedia, the free encyclopedia
Jump to: navigation, search
Simulated dark matter halo from a cosmological N-body simulation
A dark matter halo is a hypothetical component of a galaxy that envelops the galactic disc and extends well beyond the edge of the visible galaxy. The halo's mass dominates the total mass. Since they consist of dark matter, halos cannot be observed directly, but their existence is inferred through their effects on the motions of stars and gas in galaxies. Dark matter halos play a key role in current models of galaxy formation and evolution.
Galaxy rotation curve for the Milky Way. Vertical axis is speed of rotation about the galactic center. Horizontal axis is distance from the galactic center. The sun is marked with a yellow ball. The observed curve of speed of rotation is blue. The predicted curve based upon stellar mass and gas in the Milky Way is red. Scatter in observations roughly indicated by gray bars. The difference is due to dark matter or perhaps a modification of the law of gravity.[1][2][3]
Contents
[hide]
1 Rotation curves as evidence of a dark matter halo
2 Formation and structure of dark matter halos
2.1 Density profiles
2.2 Shape
2.3 Halo substructure
2.4 Angular momentum
3 Theories about the nature of dark matter
4 Milky Way dark matter halo
5 See also
6 References
7 Further reading
8 External links
Rotation curves as evidence of a dark matter halo[edit]
The presence of dark matter (DM) in the halo is inferred from its gravitational effect on a spiral galaxy's rotation curve. Without large amounts of mass throughout the (roughly spherical) halo, the rotational velocity of the galaxy would decrease at large distances from the galactic center, just as the orbital speeds of the outer planets decrease with distance from the Sun. However, observations of spiral galaxies, particularly radio observations of line emission from neutral atomic hydrogen (known, in astronomical parlance, as HI), show that the rotation curve of most spiral galaxies flattens out, meaning that rotational velocities do not decrease with distance from the galactic center.[4] The absence of any visible matter to account for these observations implies either that unobserved ("dark") matter, first proposed by Ken Freeman in 1970, exist, or that the theory of motion under gravity (General Relativity) is incomplete. Freeman noticed that the expected decline in velocity was not present in NGC 300 nor M33, and considered an undetected mass to explain it. The DM Hypothesis has been reinforced by several studies.[5][6][7][8]
Formation and structure of dark matter halos[edit]
The formation of dark matter halos is believed to have played a major role in the early formation of galaxies. During the phase of time in the universe when galaxies were first formed, the temperature of the baryonic matter should have still been much too high for it to form gravitationally self-bound objects, thus requiring the prior formation of dark matter structure to add additional gravitational interactions. The current hypothesis for this is based on cold dark matter (CDM) and its formation into structure early in the universe.
The hypothesis for CDM structure formation begins with density perturbations in the Universe that grow linearly until they reach a critical density, after which they would stop expanding and collapse to form gravitationally bound dark matter halos. These halos would continue to grow in mass (and size), either through accretion of material from their immediate neighborhood, or by merging with other halos. Numerical simulations of CDM structure formation have been found to proceed as follows: A small volume with small perturbations initially expands with the expansion of the Universe. As time proceeds, small-scale perturbations grow and collapse to form small halos. At a later stage, these small halos merge to form a single virialized dark matter halo with an ellipsoidal shape, which reveals some substructure in the form of dark matter sub-halos.[9]
The use of CDM overcomes issues associated with the normal baryonic matter because it removes most of the thermal and radiative pressures that were preventing the collapse of the baryonic matter. The fact that the dark matter is cold compared to the baryonic matter allows the DM to form these initial, gravitationally bound clumps. Once these subhalos formed, their gravitational interaction with baryonic matter is enough to overcome the thermal energy, and allow it to collapse into the first stars and galaxies. Simulations of this early galaxy formation matches the structure observed by galactic surveys as well as observation of the Cosmic Microwave Background.[10]
Density profiles[edit]
A commonly used model for galactic dark matter halos is the pseudo-isothermal halo:[11]
ρ ( r ) = ρ o [ 1 + ( r r c ) 2 ] − 1 {\displaystyle \rho (r)=\rho _{o}\left[1+\left({\frac {r}{r_{c}}}\right)^{2}\right]^{-1}}
where ρ o {\displaystyle \rho _{o}} denotes the finite central density and r c {\displaystyle r_{c}} the core radius. This provides a good fit to most rotation curve data. However, it cannot be a complete description, as the enclosed mass fails to converge to a finite value as the radius tends to infinity. The isothermal model is, at best, an approximation. Many effects may cause deviations from the profile predicted by this simple model. For example, (i) collapse may never reach an equilibrium state in the outer region of a dark matter halo, (ii) non-radial motion may be important, and (iii) mergers associated with the (hierarchical) formation of a halo may render the spherical-collapse model invalid.[12]
Numerical simulations of structure formation in an expanding universe lead to the theoretical prediction of the NFW (Navarro-Frenk-White) profile:[13]
ρ ( r ) = ρ c r i t δ c ( r r s ) ( 1 + r r s ) 2 {\displaystyle \rho (r)={\frac {\rho _{crit}\delta _{c}}{\left({\frac {r}{r_{s}}}\right)\left(1+{\frac {r}{r_{s}}}\right)^{2}}}}
where r s {\displaystyle r_{s}} is a scale radius, δ c {\displaystyle \delta _{c}} is a characteristic (dimensionless) density, and ρ c r i t {\displaystyle \rho _{crit}} = 3 H 2 / 8 π G {\displaystyle 3H^{2}/8\pi G} is the critical density for closure. The NFW profile is called 'universal' because it works for a large variety of halo masses, spanning four orders of magnitude, from individual galaxies to the halos of galaxy clusters. This profile has a finite gravitational potential even though the integrated mass still diverges logarithmically. It has become conventional to refer to the mass of a halo at a fiducial point that encloses an overdensity 200 times greater than the critical density of the universe, though mathematically the profile extends beyond this notational point. It was later deduced that the density profile depends on the environment, with the NFW appropriate only for isolated halos.[14] NFW halos generally provide a worse description of galaxy data than does the pseudo-isothermal profile, leading to the cuspy halo problem.
Higher resolution computer simulations are better described by the Einasto profile:[15]
ρ ( r ) = ρ e E x p [ − d n ( ( r r c ) 1 n − 1 ) ] {\displaystyle \rho (r)=\rho _{e}Exp\left[-d_{n}\left(\left({\frac {r}{r_{c}}}\right)^{\frac {1}{n}}-1\right)\right]}
where r is the spatial (i.e., not projected) radius. The term d n {\displaystyle d_{n}} is a function of n such that ρ e {\displaystyle \rho _{e}} is the density at the radius r e {\displaystyle r_{e}} that defines a volume containing half of the total mass. While the addition of a third parameter provides a slightly improved description of the results from numerical simulations, it is not observationally distinguishable from the 2 parameter NFW halo,[16] and does nothing to alleviate the cuspy halo problem.
Shape[edit]
The collapse of overdensities in the cosmic density field is generally aspherical. So, there is no reason to expect the resulting halos to be spherical. Even the earliest simulations of structure formation in a CDM universe emphasized that the halos are substantially flattened.[17] Subsequent work has shown that halo equidensity surfaces can be described by ellipsoids characterized by the lengths of their axes.[18]
Because of uncertainties in both the data and the model predictions, it is still unclear whether the halo shapes inferred from observations are consistent with the predictions of ΛCDM cosmology.
Halo substructure[edit]
Up until the end of the 1990s, numerical simulations of halo formation revealed little substructure. With increasing computing power and better algorithms, it became possible to use greater numbers of particles and obtain better resolution. Substantial amounts of substructure are now expected.[19][20][21] When a small halo merges with a significantly larger halo it becomes a subhalo orbiting within the potential well of its host. As it orbits, it is subjected to strong tidal forces from the host, which cause it to lose mass. In addition the orbit itself evolves as the subhalo is subjected to dynamical friction which causes it to lose energy and angular momentum to the dark matter particles of its host. Whether a subhalo survives as a self-bound entity depends on its mass, density profile, and its orbit.[22]
Angular momentum[edit]
As originally pointed out by Hoyle[23] and first demonstrated using numerical simulations by Efstathiou & Jones,[24] asymmetric collapse in an expanding universe produces objects with significant angular momentum.
Numerical simulations have shown that the spin parameter distribution for halos formed by dissipation-less hierarchical clustering is well fit by a log-normal distribution, the median and width of which depend only weakly on halo mass, redshift, and cosmology:[25]
ρ ( λ ) d λ = 1 2 π σ l n λ exp  [ − ln  ( λ λ ¯ ) 2 2 σ ln  λ 2 ] d λ λ {\displaystyle \rho (\lambda )d\lambda ={\frac {1}{{\sqrt {2\pi }}\sigma _{ln\lambda }}}\exp \left[-{\frac {\ln \left({\frac {\lambda }{\bar {\lambda }}}\right)^{2}}{2\sigma _{\ln \lambda }^{2}}}\right]{\frac {d\lambda }{\lambda }}}
with λ ¯ ≈ 0.035 {\displaystyle {\bar {\lambda }}\approx 0.035} and σ l n λ ≈ 0.5 {\displaystyle \sigma _{ln\lambda }\approx 0.5} . At all halo masses, there is a marked tendency for halos with higher spin to be in denser regions and thus to be more strongly clustered.[26]
Theories about the nature of dark matter[edit]
Main article: Dark matter
The nature of dark matter in the galactic halos of spiral galaxies is still undetermined, but there are two popular theories: either the halo is composed of weakly interacting elementary particles known as WIMPs, or it is composed of a number of small, dark bodies known as MACHOs. MACHOs, an acronym for massive compact halo objects, would be composed of “ordinary” matter that simply does not emit easily detectable radiation. The reliance of modern astronomy on detecting electromagnetic radiation would render dim, but massive objects, nearly undetectable. A wide range of possible MACHO candidates have been suggested, encompassing everything from black holes to very dim dwarf stars. Despite being too dim to detect directly via electromagnetic telescopes, MACHOs would necessarily interact gravitationally, as described by general relativity. The preferred method for searching for MACHOs in the halo of our own galaxy has been to look for microlensing events. Gravitational microlensing occurs when two stars fall on a common line of sight, rendering the far star obscured by the near one. However, as light from the far star passes through the gravitational well of the near star the light bends, creating an Einstein Halo. In a microlensing event, the halo is so small that it is optically indistinguishable from the star. The overall effect is to simply make the star appear brighter. The EROS and MACHO projects search of MACHOs in the halo by observing stars in the small and large Magellanic clouds. If a MACHO existed in the halo along the line of sight of stars in the cloud, the lensing would brighten it from that orientation as opposed to others. The magnitude and number (or lack of) lensing events can be used to place bounds on the masses of any MACHOs which might be in the halo. The two projects initially were able to place a very strict limit on MACHOS in the range of 3.5 ⋅ 10 − 7 M ⊙ < m < 4.5 ⋅ 10 − 5 M ⊙ , {\displaystyle 3.5\cdot 10^{-7}M_{\odot }<m<4.5\cdot 10^{-5}M_{\odot },} concluding that such light mass MACHOs could, at most, only constitute 10% of the accepted mass of our dark matter halo.[27] Two years later, the EROS2 project extended this limit, concluding that any MACHO less than a single solar mass could not make up a significant part of the halo.[28] The two collaborations were able to extend this to a rather large window, ruling out any MACHO in the 3.5 − 7 M ⊙ < m < 30 M ⊙ {\displaystyle 3.5^{-7}M_{\odot }<m<30M_{\odot }} window. The final window of extremely heavy MACHOs above 43 M ⊙ {\displaystyle 43M_{\odot }} were ruled out by comparing Monte Carlo method simulations to observed distributions,[29] which the authors indicate as “The End of the MACHO Era”. Extremely light MACHOs less than the current limit are also not a viable possibility, as such light mass objects would not have survived on the timescale that it would take for the galaxy to form.[30]
Milky Way dark matter halo[edit]
The visible disk of the Milky Way Galaxy is embedded in a much larger, roughly spherical halo of dark matter. The dark matter density drops off with distance from the galactic center. It is now believed that about 95% of the Galaxy is composed of dark matter, a type of matter that does not seem to interact with the rest of the Galaxy's matter and energy in any way except through gravity. The luminous matter makes up approximately 9 x 1010 solar masses. The dark matter halo is likely to include around 6 x 1011 to 3 x 1012 solar masses of dark matter.[31][32]
See also[edit]
Galaxy formation and evolution
Galactic coordinate system
Disc (galaxy)
Bulge (astronomy)
Galactic halo
Spiral arm
Dark matter
Dark galaxy
References[edit]
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Jump up ^ Mark H. Jones; Robert J. Lambourne; David John Adams (2004). An Introduction to Galaxies and Cosmology. Cambridge University Press. p. 21; Figure 1.13. ISBN 0-521-54623-0.
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Jump up ^ Bregman, K. (1987), Ph. Thesis, Univ. Groningen
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Jump up ^ Houjun Mo, Frank Van den Bosch, S. White (2010), Galaxy formation and Evolution, Cambridge University Press.
Jump up ^ Navarro, J. et al. (1997), A Universal Density Profile from Hierarchical Clustering
Jump up ^ Avila-Reese, V., Firmani, C. and Hernandez, X. (1998), Astrophys. J. 505, 37.
Jump up ^ Merritt, D. et al. (2006), Empirical Models for Dark Matter Halos. I. Nonparametric Construction of Density Profiles and Comparison with Parametric Models
Jump up ^ McGaugh, S. "et al." (2007), The Rotation Velocity Attributable to Dark Matter at Intermediate Radii in Disk Galaxies
Jump up ^ Davis, M., Efstathiou, G., Frenk, C. S., White, S. D. M. (1985), ApJ. 292, 371
Jump up ^ Franx, M., Illingworth, G., de Zeeuw, T. (1991), ApJ., 383, 112
Jump up ^ Klypin, A., Gotlöber, S., Kravtsov, A. V., Khokhlov, A. M. (1999), ApJ., 516,530
Jump up ^ Diemand, J., Kuhlen, M., Madau, P. (2007), ApJ, 667, 859
Jump up ^ Springel, V., Wang, J., Vogelsberger, M., et al. (2008), MNRAS, 391,1685
Jump up ^ Houjun Mo, Frank Van den Bosch, S. White (2010), Galaxy formation and Evolution, Cambridge University Press
Jump up ^ Hoyle, F. (1949), Problems of Cosmical Aerodynamics, Central Air Documents Office, Dayton.
Jump up ^ Efstathiou, G., Jones, B. J. T. (1979), MNRAS, 186, 133
Jump up ^ Maccio, A. V., Dutton, A. A., van den Bosch, F. C., et al. (2007), MNRAS, 378, 55
Jump up ^ Gao, L., White, S. D. M. (2007), MNRAS, 377, L5
Jump up ^ Alcock, C.; Allsman, R. A.; Alves, D.; Ansari, R.; Aubourg, É; Axelrod, T. S.; Bareyre, P.; Beaulieu, J.-Ph; Becker, A. C. (1998-01-01). "EROS and MACHO Combined Limits on Planetary-Mass Dark Matter in the Galactic Halo". The Astrophysical Journal Letters. 499 (1): L9. Bibcode:1998ApJ...499L...9A. ISSN 1538-4357. arXiv:astro-ph/9803082  . doi:10.1086/311355.
Jump up ^ Lasserre, T.; Collaboration, EROS (2000-02-11). "Not enough stellar Mass Machos in the Galactic Halo". Astronomy and Astrophysics Letters. 355: L39–L42. Bibcode:2000A&A...355L..39L. arXiv:astro-ph/0002253  .
Jump up ^ Yoo, Jaiyul; Chanamé, Julio; Gould, Andrew (2004-01-01). "The End of the MACHO Era: Limits on Halo Dark Matter from Stellar Halo Wide Binaries". The Astrophysical Journal. 601 (1): 311. Bibcode:2004ApJ...601..311Y. ISSN 0004-637X. arXiv:astro-ph/0307437  . doi:10.1086/380562.
Jump up ^ de Rujula, A.; Jetzer, P.; Masso, E. (1992-02-01). "On the Nature of the Dark Halo of Our Galaxy". Astronomy and Astrophysics. 254: 99. Bibcode:1992A&A...254...99D. ISSN 0004-6361.
Jump up ^ Battaglia et al. (2005), The radial velocity dispersion profile of the Galactic halo: constraining the density profile of the dark halo of the Milky Way
Jump up ^ Kafle, P.R.; Sharma, S.; Lewis, G.F.; Bland-Hawthorn, J. (2014). "On the Shoulders of Giants: Properties of the Stellar Halo and the Milky Way Mass Distribution". The Astrophysical Journal. 794 (1): 17. Bibcode:2014ApJ...794...59K. arXiv:1408.1787  . doi:10.1088/0004-637X/794/1/59.
Further reading[edit]
Bertone, Gianfranco (2010). Particle Dark Matter: Observations, Models and Searches. Cambridge University Press. p. 762. ISBN 978-0-521-76368-4.
Brainerd, Tereasa (July 2011). "How are Bright Galaxies Embedded within their Dark Matter Halos?". Astronomical Review. 6 (7). Retrieved 11 October 2012.
External links[edit]
Rare Blob Unveiled: Evidence For Hydrogen Gas Falling Onto A Dark Matter Clump? European Southern Observatory (ScienceDaily) July 3, 2006
Dark Matter Search Experiment , PICASSO Experiment
Black Holes and Dark matter
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