ORCID Profile
0000-0002-4912-9388
Current Organisation
Centre de recherche astrophysique de Lyon
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Publisher: Oxford University Press (OUP)
Date: 18-02-2020
Publisher: Oxford University Press (OUP)
Date: 24-12-2019
Abstract: We present results of the MUSE-ALMA haloes, an ongoing study of the circumgalactic medium (CGM) of low-redshift galaxies (z ≤ 1.4), currently comprising 14 strong H i absorbers in 5 quasar fields. We detect 43 galaxies associated with absorbers down to star formation rate (SFR) limits of 0.01–0.1 M⊙ yr−1, found within impact parameters (b) of 250 kpc from the quasar sightline. Excluding the targeted absorbers, we report a high detection rate of 89 per cent and find that most absorption systems are associated with pairs or groups of galaxies (3–11 members). We note that galaxies with the smallest impact parameters are not necessarily the closest to the absorbing gas in velocity space. Using a multiwavelength data set (UVES/HIRES, HST, MUSE), we combine metal and H i column densities, allowing for derivation of the lower limits of neutral gas metallicity as well as emission-line diagnostics (SFR, metallicities) of the ionized gas in the galaxies. We find that groups of associated galaxies follow the canonical relations of N(H i)–b and Wr(2796)–b, defining a region in parameter space below which no absorbers are detected. The metallicity of the ISM of associated galaxies, when measured, is higher than the metallicity limits of the absorber. In summary, our findings suggest that the physical properties of the CGM of complex group environments would benefit from associating the kinematics of in idual absorbing components with each galaxy member.
Publisher: American Astronomical Society
Date: 05-02-2019
Publisher: Oxford University Press (OUP)
Date: 12-06-2021
Abstract: We report on the stellar content, half-light radii and star formation rates of a s le of 10 known high-redshift (z ≳ 2) galaxies selected on strong neutral hydrogen (H i) absorption ($\\log ({\\rm N_{H\\, \\rm {I}}\\: /\\: cm}^{-2})\\,\\gt\\, 19$) towards background quasars. We use observations from the Hubble Space Telescope Wide Field Camera 3 in three broad-band filters to study the spectral energy distribution (SED) of the galaxies. Using careful quasar point spread function subtraction, we study their galactic environments, and perform the first systematic morphological characterization of such absorption-selected galaxies at high redshifts. Our analysis reveals complex, irregular hosts with multiple star-forming clumps. At a spatial s ling of 0.067 arcsec per pixel (corresponding to 0.55 kpc at the median redshift of our s le), 40 per cent of our s le requires multiple Sérsic components for an accurate modelling of the observed light distributions. Placed on the mass–size relation and the ‘main sequence’ of star-forming galaxies, we find that absorption-selected galaxies at high redshift extend known relations determined from deep luminosity-selected surveys to an order of magnitude lower stellar mass, with objects primarily composed of star-forming, late-type galaxies. We measure half-light radii in the range r1/2 ∼ 0.4 to 2.6 kpc based on the reddest band (F160W) to trace the oldest stellar populations, and stellar masses in the range log (M⋆/M⊙) ∼ 8 to 10 derived from fits to the broad-band SED. Spectroscopic and SED-based star formation rates are broadly consistent, and lie in the range $\\log (\\mathrm{SFR}/{\\rm M}_{\\odot }\\, {\\rm yr}^{-1}) \\sim 0.0$ to 1.7.
Publisher: Oxford University Press (OUP)
Date: 16-03-2011
Publisher: EDP Sciences
Date: 27-11-2015
Publisher: American Astronomical Society
Date: 27-12-2019
Publisher: EDP Sciences
Date: 2017
DOI: 10.1051/0004-6361/201629173
Abstract: We present the discovery of a molecular cloud at z abs ≈ 2.5255 along the line of sight to the quasar SDSS J 000015.17+004833.3. We use a high-resolution spectrum obtained with the Ultraviolet and Visual Echelle Spectrograph together with a deep multi-wavelength medium-resolution spectrum obtained with X-shooter (both on the Very Large Telescope) to perform a detailed analysis of the absorption lines from ionic, neutral atomic and molecular species in different excitation levels, as well as the broad-band dust extinction. We find that the absorber classifies as a D ed Lyman- α system (DLA) with log N (H i ) (cm -2 ) = 20.8 ± 0.1. The DLA has super-solar metallicity ( Z ~ 2.5 Z ⊙ , albeit to within a factor of two to three) with a depletion pattern typical of cold gas and an overall molecular fraction f = 2 N (H 2 )/(2 N (H 2 ) + N (H i )) ~ 50%. This is the highest f -value observed to date in a high- z intervening system. Most of the molecular hydrogen arises from a clearly identified narrow ( b ~ 0.7km s -1 ), cold component in which carbon monoxide molecules are also found, with log N (CO)≈ 15. With the help of the spectral synthesis code Cloudy, we study the chemical and physical conditions in the cold gas. We find that the line of sight probes the gas deep after the H i -to-H 2 transition in a ~4−5 pc-size cloud with volumic density n H ~ 80 cm -3 and temperature of only 50 K. Our model suggests that the presence of small dust grains (down to about 0.001 μ m) and high cosmic ray ionisation rate ( ζ H ~ a few times 10 -15 s -1 ) are needed to explain the observed atomic and molecular abundances. The presence of small grains is also in agreement with the observed steep extinction curve that also features a 2175 Å bump. Interestingly, the chemical and physical properties of this cloud are very similar to what is seen in diffuse molecular regions of the nearby Perseus complex, despite the former being observed when the Universe was only 2.5 Gyr old. The high excitation temperature of CO rotational levels towards J0000+0048 betrays however the higher temperature of the cosmic microwave background. Using the derived physical conditions, we correct for a small contribution (0.3 K) of collisional excitation and obtain T CMB ( z = 2.53) ≈ 9.6 K, in perfect agreement with the predicted adiabatic cooling of the Universe.
No related grants have been discovered for Jens-Kristian Krogager.