View source for Faint Images of the Radio Sky at Twenty-Centimeters

{{Infobox astronomical survey}}
'''Faint Images of the Radio Sky at Twenty-Centimeters''', or '''FIRST''', was an [[astronomical survey]] of the [[Northern Hemisphere]] carried out by the [[Karl G. Jansky Very Large Array|Very Large Array]]. It was led by [[Robert H. Becker]], [[Richard L. White]], and [[David J. Helfand]], who came up with the idea for the survey after they had completed the [[VLA Galactic Plane survey]] in 1990,<ref name="Becker1994" /> as well as [[Michael D. Gregg]] and [[Sally A. Laurent-Muehleisen]].<ref name="website" /> The survey was started 50 years after the first systematic survey of the radio sky was completed by [[Grote Reber]] in April 1943.<ref name="Becker1995" />

== Survey ==
The survey covers 10,575 [[square degrees]],<ref name="cat2014" /> around 25% of the sky,<ref name="Becker1994" /> with regions centred on the North and South [[Galactic pole]]s. The regions were chosen so that they would also be covered by the [[Sloan Digital Sky Survey]] (SDSS) in 5 optical bands,<ref name="survey" /> and the survey was comparable to the [[National Geographic Society – Palomar Observatory Sky Survey|Palomar Observatory Sky Survey]] in terms of resolution and sensitivity.<ref name="Becker1995" />

The observations were made in 'B' configuration at a wavelength of {{convert|20|cm|MHz}} (in the [[L-band#Astronomy|L Band]]), with an [[angular resolution]] of 5 [[arcsecond]].<ref name="Skyview">{{cite web | url=https://skyview.gsfc.nasa.gov/current/cgi/survey.pl#FIRST | title=SkyView surveys }}</ref> It was proposed at the same time as the [[NRAO VLA Sky Survey]], and trial observations for both surveys were taken in 1992. Survey observations of the North Galactic pole started in 1993,<ref name="Becker1994" /> with 144 hours of observing time in April and May 1993 for test observations and the initial survey strip of 300 square degrees, producing an initial catalogue of 28,000 sources.<ref name="Becker1995" /> Survey observations continued until 2004. Observations of the South Galactic pole were made in 2009 and 2011;<ref name="survey" /> the 2011 observations used the [[EVLA]].<ref name="new" /> The target flux density limit was 1 [[Jansky|milliJansky]], with an <0.15mJy [[r.m.s.]] noise limit.<ref name="Becker1995" />

The survey data was analysed using an automated pipeline through the [[Astronomical Image Processing System]].<ref name="Becker1994" /> Images and catalogues from the survey were made available after quality checks, without a proprietary period.<ref name="description" /> Several versions of the survey catalogue have been generated, with the first published in 1997,<ref name="White1997" /> and the latest ({{as of|2017|lc=y}}) published in December 2014.<ref name="cat2014" /> The catalogue includes over 70,000 cross-identifications with SDSS and the [[2MASS|Two Micron All Sky Survey (2MASS)]].<ref name="new" /> The expectation was that <math>10^6</math> radio sources would be observed and 65,000 images produced by the survey;<ref name="Becker1994" /> the 2014 catalogue included 946,432 sources.<ref name="cat2014" />  Sources in the catalogue follow a naming convention comprising the survey name and source coordinate with the format "'''FIRST J'''hhmmss.s+ddmmss"; the convention is registered with the [[International Astronomical Union]].<ref name="convention" />

== Science ==
The resolution of the survey was chosen so that optical counterparts to the radio sources could be identified; complex radio sources with multiple components could be resolved (to avoid optical misidentifications); and radio morphology (''e.g.'', [[Fanaroff-Riley classification]]) could be identified.<ref name="Becker1994" /> The survey aimed to contribute to science on [[quasar]]s and [[active galaxy|active galaxies]]; [[galaxy evolution]]; [[galactic astronomy]]; the [[large-scale structure of the Universe]]; and [[dark matter]].<ref name="Becker1994" /> The survey produced a series of papers.<ref name="publications" /> The survey paper has been referenced by over 1,600 other scientific publications.<ref name="Becker1995" />

The survey sources were cross-matched with the Palomar Sky Survey to create the FIRST Bright Quasar Survey (FBQS), which comprised quasar candidates that were then followed up with optical spectroscopy. The initial survey found 69 quasars, with 51 being newly identified.<ref name="Gregg1996" /> A number of [[broad absorption line]] quasars were discovered by FIRST.<ref name="Becker1997" /><ref name="Brotherton1998" /> Other, high-redshift quasars were identified in the survey by cross-matching with SDSS.<ref name="McGreer2009" />

Variability was detected in over 1600 sources during the course of the survey, including stars, [[pulsar]]s, galaxies, quasars, and unidentified radio sources.<ref name="Thyagarajan2011" />  On large scales, the [[Correlation function (astronomy)|two-point correlation function]] between radio galaxies was observed.<ref name="Cress1996" />

== References ==
{{Reflist|30em|refs=
<ref name="Becker1994">{{cite journal|last1=Becker|first1=Robert H.|last2=White|first2=Richard L.|last3=Helfand|first3=David J.|title=The VLA's FIRST Survey|journal=ASP Conference Series|date=1 January 1994|volume=61|pages=165|bibcode=1994ASPC...61..165B}}</ref>
<ref name="publications">{{cite web|title=The VLA FIRST Survey: Publications|url=http://sundog.stsci.edu/first/publications.html|website=sundog.stsci.edu|accessdate=30 December 2016}}</ref>
<ref name="cat2014">{{cite web | url=http://sundog.stsci.edu/first/catalogs/readme_14dec17.html | title=The FIRST Survey Catalog: 14Dec17 Version | accessdate=1 January 2017}}</ref>
<ref name="survey">{{cite web | url=http://sundog.stsci.edu/first/obsstatus.html | title=Status of FIRST Survey Observations | accessdate=1 January 2017}}</ref>
<ref name="Becker1995">{{cite journal|last1=Becker|first1=Robert H.|last2=White|first2=Richard L.|last3=Helfand|first3=David J.|title=The FIRST Survey: Faint Images of the Radio Sky at Twenty Centimeters|journal=Astrophysical Journal |volume=450|pages=559|bibcode=1995ApJ...450..559B|year=1995|doi=10.1086/176166|doi-access=free}}</ref>
<ref name="new">{{cite web | url=http://sundog.stsci.edu/first/whatsnew.html | title=What's New in FIRST? | accessdate=1 January 2017}}</ref>
<ref name="convention">{{cite web | url=http://sundog.stsci.edu/first/nomenclature.html | title=Designation of FIRST Sources | accessdate=1 January 2017}}</ref>
<ref name="description">{{cite web | url=http://sundog.stsci.edu/first/description.html | title=Description of the FIRST Survey | accessdate=1 January 2017}}</ref>
<ref name="website">{{cite web | url=http://sundog.stsci.edu/ | title=The VLA FIRST Survey | accessdate=1 January 2017}}</ref>
<ref name="Gregg1996">{{cite journal|last1=Gregg|first1=Michael D.|last2=Becker|first2=Robert H.|last3=White|first3=Richard L.|last4=Helfand|first4=David J.|last5=McMahon|first5=Richard G.|last6=Hook|first6=Isobel M.|title=The First Bright QSO Survey|journal=The Astronomical Journal|date=1 August 1996|volume=112|pages=407|doi=10.1086/118024|bibcode=1996AJ....112..407G|arxiv = astro-ph/9604148 |s2cid=119330027}}</ref>
<ref name="White1997">{{cite journal|last1=White|first1=Richard L.|last2=Becker|first2=Robert H.|last3=Helfand|first3=David J.|last4=Gregg|first4=Michael D.|title=A Catalog of 1.4 GHz Radio Sources from the FIRST Survey|journal=The Astrophysical Journal|date=1 February 1997|volume=475|issue=2|pages=479–493|doi=10.1086/303564|bibcode=1997ApJ...475..479W|doi-access=}}</ref>
<ref name="Cress1996">{{cite journal|last1=Cress|first1=Catherine M.|last2=Helfand|first2=David J.|last3=Becker|first3=Robert H.|last4=Gregg|first4=Michael D.|last5=White|first5=Richard L.|title=The Angular Two-Point Correlation Function for the FIRST Radio Survey|journal=The Astrophysical Journal|date=1 December 1996|volume=473|pages=7–14|doi=10.1086/178122|bibcode=1996ApJ...473....7C|arxiv = astro-ph/9606176 |s2cid=62068}}</ref>
<ref name="Becker1997">{{cite journal|last1=Becker|first1=Robert H.|last2=Gregg|first2=Michael D.|last3=Hook|first3=Isobel M.|last4=McMahon|first4=Richard G.|last5=White|first5=Richard L.|last6=Helfand|first6=David J.|title=The FIRST Radio-loud Broad Absorption Line QSO and Evidence for a Hidden Population of Quasars|journal=The Astrophysical Journal Letters|date=1 April 1997|volume=479|issue=2|pages=L93–L96|doi=10.1086/310594|bibcode=1997ApJ...479L..93B|arxiv = astro-ph/9702012 |s2cid=14603492}}</ref>
<ref name="Brotherton1998">{{cite journal|last1=Brotherton|first1=Michael S.|last2=van Breugel|first2=Wil|last3=Smith|first3=R. J.|last4=Boyle|first4=B. J.|last5=Shanks|first5=T.|last6=Croom|first6=S. M.|last7=Miller|first7=Lance|last8=Becker|first8=Robert H.|title=Discovery of Radio-Loud Broad Absorption Line Quasars Using Ultraviolet Excess and Deep Radio Selection|journal=The Astrophysical Journal Letters|date=1 September 1998|volume=505|issue=1|pages=L7–L10|doi=10.1086/311599|bibcode=1998ApJ...505L...7B|arxiv = astro-ph/9807230 |s2cid=15625175}}</ref>
<ref name="Thyagarajan2011">{{cite journal|last1=Thyagarajan|first1=Nithyanandan|last2=Helfand|first2=David J.|last3=White|first3=Richard L.|last4=Becker|first4=Robert H.|title=Variable and Transient Radio Sources in the FIRST Survey|journal=The Astrophysical Journal|date=1 November 2011|volume=742|issue=1|pages=49|doi=10.1088/0004-637X/742/1/49|bibcode=2011ApJ...742...49T|arxiv = 1107.5901 |s2cid=118394490}}</ref>
<ref name="McGreer2009">{{cite journal|last1=McGreer|first1=Ian D.|last2=Helfand|first2=David J.|last3=White|first3=Richard L.|title=Radio-Selected Quasars in the Sloan Digital Sky Survey|journal=The Astronomical Journal|date=1 December 2009|volume=138|issue=6|pages=1925–1937|doi=10.1088/0004-6256/138/6/1925|bibcode=2009AJ....138.1925M|arxiv = 0909.4091 |s2cid=8989100}}</ref>
}}

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