J/A+A/698/A116 Galaxies towards SDSS J161940.56+254323.0 (Pessa+, 2025)
A positive correlation between broad HI Lyα absorptions and local
overdensities of galaxies.
Pessa I., Tejos N., Martinez-Acosta K., Lopez S., Werk J., Prochaska J.X.
<Astron. Astrophys. 698, A116 (2025)>
=2025A&A...698A.116P 2025A&A...698A.116P (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies ; Redshifts ; Photometry, SDSS ; Spectrophotometry
Keywords: methods: observational - galaxies: general - intergalactic medium -
quasars: absorption lines
Abstract:
A large fraction of the baryon budget at z<1 resides in large-scale
filaments in the form of diffuse intergalactic gas, and numerous
studies have reported a significant correlation between the strength
of the absorptions produced by this gas in the spectra of bright
background sources, and impact the parameter to cosmic filaments
intersected by these sightlines. However, a similar relation is harder
to determine for the warm-hot phase of the intergalactic gas, since
its higher Doppler parameter and significantly lower neutral gas
fraction makes this gas difficult to detect in absorption. We use a
sample of 13 broad Lyα absorbers (BLAs) detected in the HST/COS
spectrum of a single QSO (z∼0.2685), whose sightline intersects
several intercluster axes, to study the relation between BLAs and the
large-scale structure of the Universe. Given their Doppler parameters
of b>40km/s, BLAs are good tracers of warm-hot intergalactic gas. We
use VLT/MUSE and VLT/VIMOS data to infer local overdensities of
galaxies at the redshifts of the BLAs, and to assess the potential
association of the BLAs with nearby galaxies. We find that out of the
13 BLAs in our sample, four are associated with a strong overdensity
of galaxies, and four with tentative overdensities. The remaining five
are located at redshifts where we do not identify any excess of
galaxies. We find that these overdensities of galaxies at the redshift
of BLAs (±1000km/s) are local, and they vanish when larger cosmic
volumes are considered, in terms of a larger velocity offset to the
BLA or larger impact parameter to the QSO sightline. Finally, we find
a positive correlation between the total hydrogen column densities
inferred from the BLAs, and the relative excess of galaxies at the
same redshifts, consistent with the picture in which warm-hot gas
resides deep within the gravitational potential well of cosmic
filaments.
Description:
We have built a survey of galaxies around the sightline towards the
QSO SDSS J161940.56+254323.0, in order to identify galaxies potentially
associated with absorption features found in the QSO spectrum, as well
as to study the large-scale structure of the Universe at the redshift
where these absorption features are located.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 78 40 Sources in our VLT/MUSE survey
tablec1.dat 84 244 Sources in our VLT/VIMOS survey
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See also:
V/154 : Sloan Digital Sky Surveys (SDSS), Release 16 (DR16) (Ahumada+, 2020)
Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- ID [1/40] ID of source
3 A1 --- n_ID [*] Note on ID (for ID=14) (1)
5- 23 A19 --- Name Name of the object, JHHMMSS.ss+DDMMSS.s
25- 33 F9.5 deg RAdeg Right ascension (J2000)
35- 42 F8.5 deg DEdeg Declination (J2000)
44- 45 I2 arcsec b Impact parameter to the QSO
SDSS J161940.56+254323.0 sightline, in arcsec
47- 49 I3 kpc bkpc ?=- Impact parameter to the QSO
SDSS J161940.56+254323.0 sightline, in kpc
51- 54 F4.1 mag rmag ?=- r apparent magnitude computed from
the MUSE data (AB) (2)
56- 60 F5.1 mag rMAG ?=- Absolute r magnitude
62- 67 F6.4 --- z Redshift (3)
69- 74 A6 --- Class Spectral classification of each galaxy (4)
76 A1 --- Rel Reliability assigned to the redshift
classification
78 A1 --- n_Rel [t] Note on reliability (5)
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Note (1): * means that the galaxy with ID=14 is a galaxy determined to be close
to one of the BLAs in the sample (a galaxy of special importance in the paper
discussion).
Note (2): Sources where r is undefined were not detected by SExtractor and we
used MUSELET to identify them and include them in the survey.
Note (3): The uncertainties in the redshift measurements are of the order
of ∼0.0001.
Note (4): Sources were classified according to their spectral type. SF galaxies
show strong emission lines and a blue continuum and non-SF galaxies show a
strong red continuum and an absence of emission lines.
Note (5): t means Redmonster did not converge to a z on these sources;
redshifts were assigned by a visual inspection.
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Byte-by-byte Description of file: tablec1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- ID [1/244] ID of source
5- 23 A19 --- Name Name of the object, JHHMMSS.ss+DDMMSS.s
25- 33 F9.5 deg RAdeg Right ascension (J2000)
35- 42 F8.5 deg DEdeg Declination (J2000)
44- 46 I3 arcsec b Impact parameter to the QSO
SDSS J161940.56+254323.0 sightline, in arcsec
48- 52 I5 kpc bkpc ?=- Impact parameter to the QSO
SDSS J161940.56+254323.0 sightline, in kpc
54- 57 F4.1 mag gmag ?=- g apparent magnitude taken from the
SDSS DR16 survey
59- 62 F4.1 mag rmag ?=- r apparent magnitude taken from the
SDSS DR16 survey
64- 67 F4.1 mag imag ?=- i apparent magnitude taken from the
SDSS DR16 survey
69- 73 F5.1 mag iMAG ?=- Rest-frame i-band absolute magnitude (1)
75- 80 F6.4 --- z Redshift (2)
82 A1 --- Rel Reliability assigned to the redshift
classification
84 A1 --- n_Rel Note on reliability (3)
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Note (1): For galaxies at z<0.5, the k-correction was calculated using the code
available in http://kcor.sai.msu.ru.
Note (2): The uncertainties in the redshift measurements are of the order
of ∼0.0001.
Note (3): t means Redmonster did not converge to a z on these sources;
redshifts were assigned by a visual inspection.
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Acknowledgements:
Ismael Pessa, ipessa(at)aip.de
(End) Patricia Vannier [CDS] 22-Apr-2025