J/A+A/643/A6 Lyα-[CII] velocity offsets in MS galaxies (Cassata+, 2020)
The ALPINE-ALMA [CII] survey. Small Lyα-[CII] velocity offsets in
main-sequence galaxies at 4.4 < z < 6.
Cassata P., Morselli L., Faisst A., Ginolfi M., Bethermin M., Capak P.,
Le Fevre O., Schaerer D., Silverman J., Yan L., Lemaux B.C., Romano M.,
Talia M., Bardelli S., Boquien M., Cimatti A., Dessauges-Zavadsky M.,
Fudamoto Y., Fujimoto S., Giavalisco M., Hathi N.P., Ibar E., Jones G.,
Koekemoer A.M., Mendez-Hernandez H., Mancini C., Oesch P.A., Pozzi F.,
Riechers D.A., Rodighiero G., Vergani D., Zamorani G., Zucca E.
<Astron. Astrophys., 643, A6 (2020)>
=2020A&A...643A...6C 2020A&A...643A...6C (SIMBAD/NED BibCode)
ADC_Keywords: Surveys ; Interstellar medium ; Galaxy catalogs ; Redshifts ;
Millimetric/submm sources ; Infrared
Keywords: galaxies: ISM - galaxies: high-redshift - submillimeter: galaxies
Abstract:
The Lyman-α line in the ultraviolet (UV) and the [CII] line in
the far-infrared (FIR) are widely used tools to identify galaxies in
the early Universe and to obtain insights into interstellar medium
(ISM) properties in high-redshift galaxies. By combining data obtained
with ALMA in band 7 at ∼320GHz as part of the ALMA Large Program to
INvestigate [CII] at Early Times (ALPINE) with spectroscopic data from
DEIMOS at the Keck Observatory, VIMOS and FORS2 at the Very Large
Telescope, we assembled a unique sample of 53 main-sequence
star-forming galaxies at 4.4<z<6 in which we detect both the
Lyman-α line in the UV and the [CII] line in the FIR.
The goal of this paper is to constrain the properties of the Lyα
emission in these galaxies in relation to other properties of the ISM.
We used [CII], observed with ALMA, as a tracer of the systemic
velocity of the galaxies, and we exploited the available optical
spectroscopy to obtain the Lyα-[CII] and ISM-[CII] velocity
offsets.
We find that 90% of the selected objects have Lyα-[CII] velocity
offsets in the range 0<ΔvLyα-[CII]<400km/s, in line with
the few measurements available so far in the early Universe, and
significantly smaller than those observed at lower redshifts. At the
same time, we observe ISM-[CII] offsets in the range
-500<ΔvISM-[CII]<0km/s, in line with values at all redshifts,
which we interpret as evidence for outflows in these galaxies. We find
significant anticorrelations between ΔvLyα-[CII] and the
Lyα rest-frame equivalent width EW0(Lyα) (or
equivalently, the Lyα escape fraction fesc(Lyα)):
galaxies that show smaller ΔvLyα-[CII] have larger
EW0(Lyα) and fesc(Lyα).
We interpret these results in the framework of available models for
the radiative transfer of Lyα photons. According to the models,
the escape of Lyα photons would be favored in galaxies with high
outflow velocities, producing large EW0(Lyα) and small
ΔvLyα-[CII], in agreement with our observations. The
uniform shell model would also predict that the Lyα escape in
galaxies with slow outflows (0<vout<300km/s) is mainly determined by
the neutral hydrogen column density (NHI) along the line of sight,
while the alternative model by Steidel et al. (2010ApJ...717..289S 2010ApJ...717..289S)
would more highly favor a combination of NHI at the systemic velocity
and covering fraction as driver of the Lyα escape. We suggest
that the increase in Lyα escape that is observed in the
literature between z∼2 and z∼6 is not due to a higher incidence of
fast outflows at high redshift, but rather to a decrease in average
NHI along the line of sight, or alternatively, a decrease in HI
covering fraction.
Description:
We investigate the kinematics and the physical properties of the ISM
in a sample of 53 main-sequence star-forming galaxies at 4.4<z<6, for
which we exploit observations of the [CII] 158uline that are
available as part of the ALMA Large Program to INvestigate [CII] at
Early Times (ALPINE; Cat. J/A+A/643/A2), coupled with rich
spectroscopic and photometric data. In particular, we analyze the
offset between the Lyα line and ISM lines with respect to the
systemic velocity, for which [CII] can be used as proxy.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tableb1.dat 92 53 Properties of the sample from multiwavelength
photometry
tableb2.dat 79 53 Lyα, [CII], and ISM measurements for
the sample
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See also:
J/A+A/643/A2 : ALPINE DR1 merged catalog (Bethermin+, 2020)
Byte-by-byte Description of file: tableb1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 13 A13 --- ID Name (G1)
15- 19 F5.2 [Msun] log(M) Mass
21- 24 F4.2 [Msun] E_log(M) Error on Mass (upper value)
26- 29 F4.2 [Msun] e_log(M) Error on Mass (lower value)
31- 34 F4.2 [Msun/yr] logSFR Star formation rate
36- 39 F4.2 [Msun/yr] E_logSFR Error on logSFR (upper value)
41- 44 F4.2 [Msun/yr] e_logSFR Error on logSFR (lower value)
46- 49 F4.2 mag E(B-V) Extinction
51- 56 F6.2 mag MFUV Absolute FUV magnitude
58- 61 F4.2 mag E_MFUV Error on MFUV (upper value)
63- 66 F4.2 mag e_MFUV Error on MFUV (lower value)
68- 89 A22 --- Name Name as in ALPINE DR1 catalog
(Cat. J/A+A/643/A2)
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Byte-by-byte Description of file: tableb2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 13 A13 --- ID Name (G1)
15- 18 F4.1 --- S/N([CII]) Signal-to-noise from [CII]
20- 24 F5.1 0.1nm EW0(Lya) Lyα equivalent width
26- 29 F4.1 0.1nm e_EW0(Lya) rms uncertainty on EW0(Lya)
31- 34 F4.2 --- fesc(Lya) Lyα escape fraction
36- 39 F4.2 --- E_fesc(Lya) Error on fesc(Lya) (upper value)
41- 44 F4.2 --- e_fesc(Lya) Error on fesc(Lya) (lower value)
46- 51 F6.4 --- z[CII] Redshift from [CII] line
53- 58 F6.4 --- e_z[CII] rms uncertainty on z[CII]
60- 62 I3 km/s DLya Lyα velocity offset
64- 66 I3 km/s e_DLya rms uncertainty on DLya
68- 71 I4 km/s DISM ? ISM velocity offset
73- 75 I3 km/s E_DISM ? Error on ISM (upper value)
77- 79 I3 km/s e_DISM ? Error on ISM (lower value)
--------------------------------------------------------------------------------
Global notes:
Note (G1): Names starting with CG indicate objects in the CANDELS GOODS South
area; Names starting with vc indicate objects with VUDS VIMOS/VLT spectra in
the COSMOS field; DC indicates objects with DEIMOS spectra in the COSMOS field.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
References:
Faisst et al., 2020ApJS..247...61F 2020ApJS..247...61F,
The ALPINE-ALMA [CII] survey: Multiwavelength ancillary data and basic
physical measurements
Le Fevre et al. 2020A&A...643A...1L 2020A&A...643A...1L, arXiv:1910.09517,
The ALPINE-ALMA [CII] survey. Survey strategy, observations, and sample
properties of 118 star-forming galaxies at 4<z<6
Fujimoto et al. 2020ApJ...900....1F 2020ApJ...900....1F, arXiv:2003.00013
The ALPINE-ALMA [CII] survey: Size of individual star-forming galaxies
at z=4-6 and their extended halo structure
Schaerer et al., 2020A&A...643A...3S 2020A&A...643A...3S
The ALPINE-ALMA [CII] survey. Little to no evolution in the [CII]-SFR
relation over the last 13 Gyr
Fudamoto et al., 2020A&A...643A...4F 2020A&A...643A...4F
The ALPINE-ALMA [CII] survey: Dust attenuation properties and obscured
star formation at z∼4.4-5.8
Dessauges-Zavadsky et al., 2020A&A...643A...5D 2020A&A...643A...5D, arXiv:2004.10771,
The ALPINE-ALMA [CII] survey: Molecular gas budget in the Early Universe
as traced by [CII]
Cassata et al., 2020A&A...643A...6C 2020A&A...643A...6C
The ALPINE-ALMA [CII] survey. Small Lyalpha-[CII] velocity offsets in
main-sequence galaxies at 4.4<z<6
Ginolfi et al., 2020A&A...643A...7G 2020A&A...643A...7G, arXiv:2004.13737,
The ALPINE-ALMA [CII] survey. Circumgalactic medium pollution and gas
mixing by tidal stripping in a merging system at z∼4.57
Gruppioni et al., 2020A&A...643A...8G 2020A&A...643A...8G, arXiv:2006.04974,
The ALPINE-ALMA [CII] survey: nature, luminosity function and star
formation history of continuum non-target galaxies up to z∼6
Khusanova et al., 2020, A&A in press, arXiv:2007.08384,
The ALPINE-ALMA [CII] Survey: Obscured star formation rate density and
main sequence of star-Forming galaxies at z>4
Loiacono et al., 2020, A&A in press, arXiv:2006.04837,
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[CII] line emitters at z∼5
Yan et al, 2020ApJ...905..147Y 2020ApJ...905..147Y, arXiv:2006.04835,
The ALPINE-ALMA [CII] survey: [CII]158micron emission line luminosity
functions at z∼4-6
Fudamoto et al., 2020, A&A in press, arXiv:2004.10760
The ALPINE-ALMA [CII] survey: Dust attenuation properties and obscured
star-formation at z∼4.4-5.8
Romano et al., 2020MNRAS.496..875R 2020MNRAS.496..875R, arXiv:2002.00961,
The ALPINE-ALMA [CII] survey: On the nature of an extremely obscured
serendipitous galaxy
Jones et al., 2020MNRAS.491L..18J 2020MNRAS.491L..18J, arXiv:1908.07777,
The ALPINE-ALMA [CII] survey: A triple merger at z∼4.56
(End) Patricia Vannier [CDS] 20-Jan-2021