TY - JOUR
T1 - The Lyα reference sample. I. Survey outline and first results for Markarian 259
AU - Östlin, Göran
AU - Hayes, Matthew
AU - Duval, Florent
AU - Sandberg, Andreas
AU - Rivera-Thorsen, Thøger
AU - Marquart, Thomas
AU - Orlitová, Ivana
AU - Adamo, Angela
AU - Melinder, Jens
AU - Guaita, Lucia
AU - Atek, Hakim
AU - Cannon, John M.
AU - Gruyters, Pieter
AU - Herenz, Edmund Christian
AU - Kunth, Daniel
AU - Laursen, Peter
AU - Mas-Hesse, J. Miguel
AU - Micheva, Genoveva
AU - Otí-Floranes, Héctor
AU - Pardy, Stephen A.
AU - Roth, Martin M.
AU - Schaerer, Daniel
AU - Verhamme, Anne
N1 - Publisher Copyright:
© 2014. The American Astronomical Society. All rights reserved.
PY - 2014/12/10
Y1 - 2014/12/10
N2 - The Lyα Reference Sample (LARS) is a substantial program with the Hubble Space Telescope (HST) that provides a sample of local universe laboratory galaxies in which to study the detailed astrophysics of the visibility and strength of the Lyα line of neutral hydrogen. Lyα is the dominant spectral line in use for characterizing high-redshift (z) galaxies. This paper presents an overview of the survey, its selection function, and HST imaging observations. The sample was selected from the combined GALEX+Sloan Digital Sky Survey catalog at z = 0.028-0.19, in order to allow Lyα to be captured with combinations of long-pass filters in the Solar Blind Channel (SBC) of the Advanced Camera for Surveys (ACS) onboard HST. In addition, LARS utilizes Hα and Hβ narrowband and u, b, i broadband imaging with ACS and the Wide Field Camera 3 (WFC3). In order to study galaxies in which large numbers of Lyα photons are produced (whether or not they escape), we demanded an Hα equivalent width W(Hα) ≥ 100 A˚. The final sample of 14 galaxies covers far-UV (FUV, λ ∼ 1500 A˚) luminosities that overlap with those of high-z Lyα emitters (LAEs) and Lyman break galaxies (LBGs), making LARS a valid comparison sample. We present the reduction steps used to obtain the Lyα images, including our LARS eXtraction software (LaXs), which utilizes pixel-by-pixel spectral synthesis fitting of the energy distribution to determine and subtract the continuum at Lyα. We demonstrate that the use of SBC long-pass-filter combinations increase the signal-to-noise ratio by an order of magnitude compared to the nominal Lyα filter available in SBC. To exemplify the science potential of LARS, we also present some first results for a single galaxy, Mrk 259 (LARS #1). This irregular galaxy shows bright and extended (indicative of resonance scattering) but strongly asymmetric Lyα emission. Spectroscopy from the Cosmic Origins Spectrograph on board HST centered on the brightest UV knot shows a moderate outflow in the neutral interstellar medium (probed by low ionization stage absorption features) and Lyα emission with an asymmetric profile. Radiative transfer modeling is able to reproduce the essential features of the Lyα line profile and confirms the presence of an outflow. From the integrated photometry we measure an Lyα luminosity of LLyα = 1.3 x 1042 erg s-1 an equivalent width W(Lyα) = 45 A˚ and an FUV absolute magnitude MFUV = -19.2 (AB). Mrk 259 would hence be detectable in high-z Lyα and LBG surveys. The total Lyα escape fraction is 12%. This number is higher than the low-z average, but similar to that at z > 4, demonstrating that LARS provides a valid comparison sample for high-z galaxy studies.
AB - The Lyα Reference Sample (LARS) is a substantial program with the Hubble Space Telescope (HST) that provides a sample of local universe laboratory galaxies in which to study the detailed astrophysics of the visibility and strength of the Lyα line of neutral hydrogen. Lyα is the dominant spectral line in use for characterizing high-redshift (z) galaxies. This paper presents an overview of the survey, its selection function, and HST imaging observations. The sample was selected from the combined GALEX+Sloan Digital Sky Survey catalog at z = 0.028-0.19, in order to allow Lyα to be captured with combinations of long-pass filters in the Solar Blind Channel (SBC) of the Advanced Camera for Surveys (ACS) onboard HST. In addition, LARS utilizes Hα and Hβ narrowband and u, b, i broadband imaging with ACS and the Wide Field Camera 3 (WFC3). In order to study galaxies in which large numbers of Lyα photons are produced (whether or not they escape), we demanded an Hα equivalent width W(Hα) ≥ 100 A˚. The final sample of 14 galaxies covers far-UV (FUV, λ ∼ 1500 A˚) luminosities that overlap with those of high-z Lyα emitters (LAEs) and Lyman break galaxies (LBGs), making LARS a valid comparison sample. We present the reduction steps used to obtain the Lyα images, including our LARS eXtraction software (LaXs), which utilizes pixel-by-pixel spectral synthesis fitting of the energy distribution to determine and subtract the continuum at Lyα. We demonstrate that the use of SBC long-pass-filter combinations increase the signal-to-noise ratio by an order of magnitude compared to the nominal Lyα filter available in SBC. To exemplify the science potential of LARS, we also present some first results for a single galaxy, Mrk 259 (LARS #1). This irregular galaxy shows bright and extended (indicative of resonance scattering) but strongly asymmetric Lyα emission. Spectroscopy from the Cosmic Origins Spectrograph on board HST centered on the brightest UV knot shows a moderate outflow in the neutral interstellar medium (probed by low ionization stage absorption features) and Lyα emission with an asymmetric profile. Radiative transfer modeling is able to reproduce the essential features of the Lyα line profile and confirms the presence of an outflow. From the integrated photometry we measure an Lyα luminosity of LLyα = 1.3 x 1042 erg s-1 an equivalent width W(Lyα) = 45 A˚ and an FUV absolute magnitude MFUV = -19.2 (AB). Mrk 259 would hence be detectable in high-z Lyα and LBG surveys. The total Lyα escape fraction is 12%. This number is higher than the low-z average, but similar to that at z > 4, demonstrating that LARS provides a valid comparison sample for high-z galaxy studies.
KW - Cosmology: observations
KW - Galaxies: evolution
KW - Galaxies: individual (Mrk 259)
KW - Galaxies: starburst
KW - Radiative transfer
KW - Ultraviolet: galaxies
UR - http://www.scopus.com/inward/record.url?scp=84914693358&partnerID=8YFLogxK
U2 - 10.1088/0004-637X/797/1/11
DO - 10.1088/0004-637X/797/1/11
M3 - Article
AN - SCOPUS:84914693358
SN - 0004-637X
VL - 797
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 1
M1 - 11
ER -