TY - JOUR
T1 - The Lyα Reference Sample.
T2 - I. SURVEY OUTLINE AND FIRST RESULTS FOR MARKARIAN 259
AU - Ostlin, Goran
AU - Hayes, Matthew
AU - Duval, Florent
AU - Sandberg, Andreas
AU - Rivera-Thorsen, Thoger
AU - Marquart, Thomas
AU - Orlitova, 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 - Oti-Floranes, Hector
AU - Pardy, Stephen A.
AU - Roth, Martin M.
AU - Schaerer, Daniel
AU - Verhamme, Anne
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
Lyαline 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 Å. The final sample of 14 galaxies covers far-UV (FUV, λ ~ 1500 Å) 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 L Lyα=1.3 × 1042 erg s–1 an equivalent width W(Lyα) = 45 Å and an FUV absolute magnitude M FUV = –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
Lyαline 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 Å. The final sample of 14 galaxies covers far-UV (FUV, λ ~ 1500 Å) 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 L Lyα=1.3 × 1042 erg s–1 an equivalent width W(Lyα) = 45 Å and an FUV absolute magnitude M FUV = –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.
U2 - 10.1088/0004-637X/797/1/11
DO - 10.1088/0004-637X/797/1/11
M3 - Journal article
SN - 0004-637X
VL - 797
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 1
M1 - 11
ER -