J/ApJ/711/928 Low-redshift Lyα galaxies from GALEX (Cowie+, 2010)
Low-redshift Lyα selected galaxies from GALEX spectroscopy: a comparison
with both UV-continuum selected galaxies and high-redshift Lyα emitters.
Cowie L.L., Barger A.J., Hu E.M.
<Astrophys. J., 711, 928-958 (2010)>
=2010ApJ...711..928C 2010ApJ...711..928C
ADC_Keywords: Galaxies, spectra ; Redshifts ; Spectra, ultraviolet ;
Equivalent widths ; Active gal. nuclei
Keywords: cosmology: observations - galaxies: abundances - galaxies: starburst
galaxies: distances and redshifts - galaxies: evolution
Abstract:
We construct a sample of low-redshift Lyα emission-line selected
sources from Galaxy Evolution Explorer (GALEX) grism spectroscopy of
nine deep fields to study the role of Lyα emission in galaxy
populations with cosmic time. Our final sample consists of 119 (141)
sources selected in the redshift interval z=0.195-0.44 (z=0.65-1.25)
from the FUV (NUV) channel. We classify the Lyα sources as
active galactic nuclei (AGNs) if high-ionization emission lines are
present in their UV spectra and as possible star-forming galaxies
otherwise. We classify additional sources as AGNs using line widths
for our Lyα emitter (LAE) analysis. These classifications are
broadly supported by comparisons with X-ray and optical spectroscopic
observations, though the optical spectroscopy identifies a small
number of additional AGNs. Defining the GALEX LAE sample in the same
way as high-redshift LAE samples, we show that LAEs constitute only
about 5% of NUV-continuum selected galaxies at z∼0.3. We also show
that they are less common at z∼0.3 than they are at z∼3. Finally, we
confirm that the z∼2 Lyman break galaxies have relatively low
metallicities for their luminosities, and we find that they lie in the
same metallicity range as the z∼0.3 Lyα galaxies.
Description:
For each targeted field, we obtained the one- and two-dimensional
spectra of all the sources with GALEX grism observations from the
Multimission Archive at STScI (MAST). The FUV spectra cover a
wavelength range of approximately 1300-1800Å at a resolution of
∼10Å, and the NUV spectra cover a wavelength range of approximately
1850-3000Å at a resolution of ∼25Å. The final Lyα selected
samples are summarized in Tables 2-10.
We made optical spectroscopic follow-up observations with the DEIMOS
spectrograph on the Keck II 10 m telescope. We obtained observations
of 39 sources randomly chosen from our GALEX candidate Lyα
Galaxy sample, 38 of which lie in the redshift interval z=0.195-0.44
and one in the redshift interval z=0.65-1.25 (Table 11), 15 sources
randomly chosen from our GALEX AGN sample (Table 12), and 124 sources
randomly chosen from our GALEX spectroscopic sample without UV
spectral identifications. For the latter, we summarize only the 47
sources found to lie in the redshift interval z=0.195-0.44 (Table 13).
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 78 69 *GALEX spectral sample identifications: GROTH 00
table3.dat 78 46 *GALEX spectral sample identifications: NGPDWS 00
table4.dat 78 39 *GALEX spectral sample identifications: CDFS 00
table5.dat 78 29 *GALEX spectral sample identifications: COSMOS 00
table6.dat 78 19 *GALEX spectral sample identifications: ELAISS1 00
table7.dat 78 22 *GALEX spectral sample identifications: SIRTFFL 00
table8.dat 78 12 *GALEX spectral sample identifications: LOCK 00
table9.dat 78 14 *GALEX spectral sample identifications: SIRTFFL 01
table10.dat 78 10 *GALEX spectral sample identifications: HDFN 00
table11.dat 82 39 DEIMOS observations: GALEX candidate Lyα
galaxies
table12.dat 77 15 DEIMOS observations: GALEX AGNs
table13.dat 77 47 DEIMOS observations: GALEX spectra without
strong Lyα emission
table14.dat 72 11 GALEX X-ray properties
table15.dat 89 62 Low-redshift GALEX LAE sample
table16.dat 84 4 Moderate-redshift GALEX LAE sample
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Note on table2.dat table[3-9].dat and table10.dat:
The nine blank high galactic latitude fields used with the deepest GALEX
grism observations are defined by the following parameters:
-----------------------------------------------------------------------
Field name RA (J2000) DE Exp NUV E(B-V) Gal Nsources LAE
(ks) lim Lat.
-----------------------------------------------------------------------
GROTH_00 214.99182 52.78173 291 21.8 0.007 59.5 1152 69
NGPDWS_00 219.15610 35.17135 156 21.5 0.009 66.2 738 46
CDFS_00 53.12779 -27.87137 149 21.5 0.008 -54.4 876 39
COSMOS_00 150.11900 2.20583 140 21.5 0.018 42.1 779 29
ELAISS1_00 9.63857 -43.99023 84 21.2 0.007 -72.9 589 19
SIRTFFL_00 259.12387 59.90915 80 21.2 0.020 35.0 800 22
LOCK_00 162.67843 58.73117 48 20.9 0.009 52.1 390 12
SIRTFFL_01 260.41425 59.34286 34 20.7 0.029 34.4 612 14
HDFN_00 189.20946 62.19772 24 20.5 0.012 54.8 265 10
-----------------------------------------------------------------------
With "Nsources" = the number of sources with spectra lying within a radius
of 32.5' from the field center and "LAE" = the number of such sources found
to have a Lyα emission line in the redshift intervals z=0.195-0.44
and z=0.65-1.25 based on their UV spectra.
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See also:
J/ApJ/703/2160 : The OPTX project. III. (Trouille+, 2009)
J/ApJS/179/1 : The OPTX project: CLANS, CLASXS and CDF-N (Trouille+, 2008)
J/ApJS/179/19 : CDFS survey: 2 Ms source catalogs (Luo+, 2008)
J/ApJ/680/1072 : Lyα-emitting galaxies at 0.2<z<0.35 (Deharveng+, 2008)
J/A+A/461/823 : Candidate Lyα emitting galaxies (Venemans+, 2007)
J/AJ/131/2373 : Extended Chandra Deep Field-South survey (Virani+, 2006)
J/ApJS/161/21 : Extended Chandra Deep Field-South survey (Lehmer+, 2005)
J/ApJ/614/75 : Lymanα emitting galaxies at z=2.38 (Francis+, 2004)
J/ApJ/738/136 : LAEs between 0.19<z<1.25 with GALEX grism (Cowie+, 2011)
J/AJ/126/539 : The Chandra Deep Fields North and South (Alexander+, 2003)
J/ApJ/508/200 : QSO low-z Lyα absorbers (Tripp+, 1998)
Byte-by-byte Description of file: table[23456789].dat table10.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- Seq [1/69] Running sequence number
3 A1 --- f_GALEX [ob] Flag on source (1)
4- 8 A5 --- --- [GALEX] Multiplicity index on GALEX name (G1)
9- 17 A9 --- GALEX GALEX name (HHMM+DDMM; J2000)
18 A1 --- m_GALEX
20- 29 F10.6 deg RAdeg Right ascension in decimal degrees (J2000)
31- 40 F10.6 deg DEdeg Declination in decimal degrees (J2000)
42- 47 F6.2 mag NUVmag ?=999 GALEX NUV magnitude
49- 54 F6.2 mag FUVmag ?=999 GALEX FUV magnitude
56- 60 F5.3 --- z Redshift
62- 66 I5 km/s Width Lyα line width
68- 71 I4 km/s e_Width The 1σ error on Width
73- 78 A6 --- Class Object type (AGN or Galaxy) from the UV spectra
--------------------------------------------------------------------------------
Note (1): Flag as follows:
o = re-measured coordinates that have a significant offset from the
cataloged position in the data archive.
b = significant enough blends to seriously affect the photometry and
coordinates.
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Byte-by-byte Description of file: table11.dat table12.dat table13.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- --- [GALEX]
6- 14 A9 --- GALEX GALEX identification (HHMM+DDMM; J2000)
15 A1 --- m_GALEX Multiplicity index on GALEX name (G1)
16- 25 F10.6 deg RAdeg Right ascension in decimal degrees (J2000)
27- 36 F10.6 deg DEdeg Declination in decimal degrees (J2000)
38- 42 F5.2 mag NUVmag GALEX NUV magnitude
44- 48 F5.2 mag gmag ? SDSS-DR6 model C g-band magnitude (not for
table 12)
50- 55 F6.4 --- zGALEX ? GALEX redshift
57- 62 F6.4 --- zsp Optical spectroscopic redshift
64- 67 I4 0.1nm EW ? Observed-frame Hα equivalent width
(not for table 12)
69- 70 I2 0.1nm e_EW ? The 1σ error on EW
72- 82 A11 --- Class Object type from the optical spectrum (Galaxy,
Seyfert 1.8/1.5 or AGN)
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Byte-by-byte Description of file: table14.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- --- [GALEX]
6- 14 A9 --- GALEX GALEX designation (HHMM+DDMM; J2000)
15 A1 --- m_GALEX Multiplicity index on GALEX name (G1)
16- 23 F8.4 deg RAdeg Right ascension in decimal degrees (J2000)
25- 32 F8.4 deg DEdeg Declination in decimal degrees (J2000)
34- 42 E9.3 mW/m2 Fhard ? Chandra flux in 2-8keV band (1)
44- 51 E8.3 mW/m2 Fsoft ? Chandra flux in 0.5-2keV band (1)
53 A1 --- l_logL Limit flag on logL
54- 58 F5.2 [10-7W] logL Chandra log of luminosity in 2-8keV band
60- 65 F6.4 --- zGALEX GALEX redshift
67- 72 A6 --- Class Object type (AGN or Galaxy)
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Note (1): We compare the CDF-N sources (Alexander et al. 2003, Cat.
J/AJ/126/539) with the HDFN 00 sources; the CLANS sources (Trouille et
al. 2008, Cat. J/ApJS/179/1, 2009, Cat. J/ApJ/703/2160) with the LOCK
00 sources; and the extended CDF-S sources (Lehmer et al. 2005, Cat.
J/ApJS/161/21; Virani et al. 2006, Cat. J/AJ/131/2373) and the 2 Ms
CDF-S sources (Luo et al. 2008, Cat. J/ApJS/179/19) with the CDFS 00
sources. See section 4 for further details.
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Byte-by-byte Description of file: table15.dat table16.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- --- [GALEX]
6- 14 A9 --- GALEX GALEX designation (HHMM+DDMM; J2000)
15 A1 --- m_GALEX Multiplicity index on GALEX name (G1)
16- 25 F10.6 deg RAdeg Right ascension in decimal degrees (J2000)
27- 36 F10.6 deg DEdeg Declination in decimal degrees (J2000)
38- 42 F5.2 mag NUVmag GALEX NUV magnitude
44- 48 F5.2 mag FUVmag GALEX FUV magnitude
50- 55 F6.4 --- zGALEX GALEX redshift
57- 61 F5.2 [10-7W] logL Log of Lyα luminosity (1)
63- 66 F4.2 [10-7W] e_logL The 1σ error on logL
68- 70 I3 0.1nm EW Rest-frame Lyα equivalent width
72- 73 I2 0.1nm e_EW The 1σ error on EW
75- 80 F6.4 --- zsp ? Ground-based redshift
81 A1 --- r_zsp [pf] Flag on zsp (2)
83- 89 A7 --- Class Optical object type (AGN, BPT AGN or SF) (3)
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Note (1): The logarithm of the Lyα luminosity,
L=4πd2Lf(Lyα), where f(Lyα) is the observed line
flux and dL is the luminosity distance.
Note (2): The ground-based redshifts are based on this paper's
observations, except for two sources in the COSMOS 00 field (p) and
two sources in the GROTH 00 field (f) which are from:
* p = Prescott et al. 2006, Cat. J/ApJ/644/100
* f = Finkelstein et al. 2009ApJ...700..276F 2009ApJ...700..276F
Note (3): For our LAE analysis we do not eliminate any sources that we
know to be AGNs from their optical spectra, since we do not have this
information for a substantial part of the sample. However, we do note
in the table where a source is clearly an AGN based on its optical
spectrum, either because it has broad lines or based on the Baldwin
et al. (1981PASP...93....5B 1981PASP...93....5B) diagnostic diagram of [OIII]5007/Hβ
versus [NII]6584/Hα. We denote these latter sources with "BPT AGN".
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Global Notes:
Note (G1): GALEX names being ambiguous, the multiplicity index m_GALEX
was added at CDS (blank for unambiguous names; a, b and c in order
of right ascension). The asterisk (*) flags the 16 duplicated sources
in table13.
Nomenclature notes:
Tables 2-16: galaxies are <[CBH2010] GALEXHHMM+DDMM> in Simbad.
History:
* 04-Apr-2012: From electronic version of the journal
* 05-Jun-2013: added the m_GALEX flag (see the "Note (G1)" above)
(End) Emmanuelle Perret [CDS] 04-Apr-2012