J/A+A/618/A184 SDSS J151349.52+035211.28 Xshooter spectra (Ranjan+, 2018)
Molecular gas and star formation in an absorption-selected galaxy:
Hitting the bull's eye at z = 2.46.
Ranjan A., Noterdaeme P., Krogager J.-K., Petitjean P., Balashev S.,
Bialy S., Srianand R., Gupta N., Fynbo J.P.U., Ledoux C., Laursen P.
<Astron. Astrophys. 618, A184 (2018)>
=2018A&A...618A.184R 2018A&A...618A.184R (SIMBAD/NED BibCode)
ADC_Keywords: QSOs ; Spectra, optical ; Spectra, ultraviolet ; Spectra, optical
Keywords: quasars: absorption lines - galaxies: high-redshift - galaxies: ISM
Abstract:
We present the detection and detailed analysis of a diffuse molecular
cloud at zabs=2.4636 towards the quasar SDSS J151349.52+035211.28
(hereafter J1513+0352) (zem~=2.68) observed with the X-shooter
spectrograph at the Very Large Telescope. We measure very high column
densities of atomic and molecular hydrogen, with
logN(HI,H2)~=21.8,21.3. This is the highest H2 column density ever
measured in an intervening damped Lyman-αsystem but we do not
detect CO, implying log N(CO)/N(H2)←7.8, which could be due to a
low metallicity of the cloud. From the metal absorption lines, we
derive the metallicity to be Z~=0.15Z☉ and determine the amount
of dust by measuring the induced extinction of the background quasar
light, AV~=0.4. We simultaneously detect Lyα emission at the
same redshift, with a centroid located at a most probable impact
parameter of only ρ~=1.4kpc. We argue that the line of sight is
therefore likely passing through the interstellar medium of a galaxy,
as opposed to the circumgalactic medium. The relation between the
surface density of gas and that of star formation seems to follow the
global empirical relation derived in the nearby Universe although our
constraints on the star formation rate and on the galaxy extent remain
too loose to be conclusive. We study the transition from atomic to
molecular hydrogen using a theoretical description based on the
microphysics of molecular hydrogen.We use the derived chemical
properties of the cloud and physical conditions (Tk~=90K and
n~=250cm-3) derived through the excitation of H2 rotational levels
and neutral carbon fine structure transitions to constrain the
fundamental parameters that govern this transition. By comparing the
theoretical and observed HI column densities, we are able to bring an
independent constraint on the incident UV flux, which we find to be in
agreement with that estimated from the observed star formation rate.
Description:
The quasar J513+0352 was observed on four different nights in service
mode, on 15-16 Apr 2015 and 14-15 May 2015 under ESO program ID
095.A-0224(A) with the multi-wavelength, medium resolution
spectrograph X-shooter mounted at the Cassegrain focus of the Very
Large Telescope UT2.
There are three tables included. The first table is the journal of
observations including the observing date, slit widths, exposure time,
seeing, airmass and position angle. The three different values for
slit widths and exposure times correspond to the UVB, VIS and NIR
arms, respectively. The exposure time for NIR data is sub-divided into
3 integrations (NDIT). Here, 'Seeing' refers to the "delivered seeing
corrected by airmass" in the VIS Band and the value of 'Airmass' is
recorded at start of exposure. The last column gives the position
angle at the start of the observations. Table 2 contains column
density details of the individual measurements of rotational levels of
H2 with errorbars. Table 3 gives the column density of each metal
component, HI and H2, and the corresponding X/H and X/Zn where 'X'
refers to individual species of metals.
Objects:
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RA (2000) DE Designation(s)
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15 13 49.52 +03 52 11.71 SDSS J151349.52+035211.28 = [VV2010] J151349.5+035211
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File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 44 12 Journal of observations
table2.dat 23 6 Column densities of H2 in different rotational
levels at zabs=2.4636 towards J1513+0352
table3.dat 40 11 Summary of column densities and abundances
list.dat 103 3 List of spectra
fits/* . 3 Individual fits spectra
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 11 A11 "date" Obs.Date Observing date
13- 15 F3.1 arcsec Width Slit width
16 A1 --- --- [(]
17- 19 A3 --- Inst Arm name (UVB, VIS or NIR)
20 A1 --- --- [)]
22- 30 A9 s ExpTime Exposure time
32- 34 F3.1 arcsec Seeing Delivered seeing corrected by airmass in
the VIS band
36- 39 F4.2 --- Airmass Airmass (recorded at start of exposure)
41- 44 I4 deg PA [] Position angle at the start of the
observation
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 11 A11 --- Species Species
14- 18 F5.2 [cm-2] logN Column density of Species
20- 23 F4.2 [cm-2] e_logN rms uncertainty on logN
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 7 A7 --- Species Species
9- 13 F5.2 [cm-2] logN Column density of Species
15- 18 F4.2 [cm-2] e_logN rms uncertainty on logN
20- 24 F5.2 [-] [X/H] ? Observed gas-phase abundances (1)
26- 29 F4.2 [-] e_[X/H] ? rms uncertainty on [X/H]
30 A1 --- n_[X/H] [f] Note on [X/H] (2)
31- 35 F5.2 [-] [X/Zn] ? Depletion relative to Zn
37- 40 F4.2 [-] e_[X/Zn] ? rms uncertainty on [X/Zn]
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Note (1): Note that since the H2 fraction is high, the total (HI+H2)
hydrogen content is considered here.
Note (2): f: Overall molecular fraction through the system
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 24 I5 --- Nx Number of points
26- 27 I2 --- Nslit Number of positions along slit in the spectrum
29- 52 A24 --- Obs.date Observation date
54- 59 F6.2 nm blambda Lower value of wavelength interval
61- 67 F7.2 nm Blambda Upper value of wavelength interval
69- 72 F4.2 nm dlambda Spectral resolution
74- 77 I4 Kibyte size Size of FITS file
79- 86 A8 --- FileName Name of FITS file, in subdirectory fits
88-103 A16 --- Title Title of the FITS file
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Acknowledgements:
Adarsh Ranjan, adarsh.ranjan(at)iap.fr
(End) Patricia Vannier [CDS] 27-Jun-2018