Consensus report on 25 yr of searches for damped Ly α galaxies in emission: confirming their metallicity–luminosity relation at z ≳ 2

Abstract

Starting from a summary of detection statistics of our recent X-shooter campaign, we review the major surveys, both space and ground based, for emission counterparts of high-redshift damped Lyα absorbers (DLAs) carried out since the first detection 25 years ago. We show that the detection rates of all surveys are precisely reproduced by a simple model in which the metallicity and luminosity of the galaxy associated to the DLA follow a relation of the form,3 ) − 20.8, and the DLA cross-section follows a relation of the form σ DLA ∝ L 0.8 . Specifically, our spectroscopic campaign consists of 11 DLAs preselected based on their equivalent width of Si II λ1526 to have a metallicity higher than [Si/H] > −1. The targets have been observed with the X-shooter spectrograph at the Very Large Telescope to search for emission lines around the quasars. We observe a high detection rate of 64% (7/11), significantly higher than the typical ∼10% for random, H I-selected DLA samples. We use the aforementioned model, to simulate the results of our survey together with a range of previous surveys: spectral stacking, direct imaging (using the 'double DLA' technique), long-slit spectroscopy, and integral field spectroscopy. Based on our model results, we are able to reconcile all results. Some tension is observed between model and data when looking at predictions of Lyα emission for individual targets. However, the object to object variations are most likely a result of the significant scatter in the underlying scaling relations as well as uncertainties in the amount of dust which affects the emission.

MUSE-ALMA haloes V: physical properties and environment of z ≤ 1.4 H i quasar absorbers

“…In Fig.8 we present the H i column density versus impact parameter. Studies so far, mostly for high H i column density absorbers (Krogager et al 2017;Augustin et al 2018), showed an anti-correlation between N(H i) and impact parameter, which is also reproduced by the OWLS hydrodynamical simulations (Rahmati & Schaye 2014): the larger the N(H i) column densities the smaller the impact parameter. Including all galaxies associated with absorbers, we are retrieving this relation also at lower H i column densities (from 10 18 to 10 21.7 cm −2 ).…”

“…Supplementary to the wide-field search was the method of using a narrow-band optical filter (about 10Å) centred around the expected [O ii] emission at the absorbers redshift (Yanny et al 1987(Yanny et al , 1989(Yanny et al , 1990aMøller & Warren 1993). Another detection method involved surveying the quasar field with a X-Shooter slit triangulation in search for associated galaxies (Møller et al 2004;Krogager et al 2017). Narrow filter integral field searches, using an array of optic fibers, for extended emission near QSOs with absorbers were also attempted (Yanny et al 1990b).…”

Direct Measurement of the [C i] Luminosity to Molecular Gas Mass Conversion Factor in High-redshift Star-forming Galaxies

“…While GRB and quasar absorption-selected galaxies by selection do not probe the same field galaxies as emission-selected surveys, there is recent evidence that they sample the same underlying star-forming galaxy population, though typically at the faint, low-mass end Krogager et al 2017). Independent of the nature of the galaxies, simulations seem to suggests that the metallicity is the primary factor regulating the abundances of [C i] or CO relative to H 2 in molecular clouds (Wolfire et al 2010;Bolatto et al 2013;Glover & Clark 2016).…”

CO-dark molecular gas at high redshift: very large H2 content and high pressure in a low-metallicity damped Lyman alpha system

“…Detecting more direct markers of star formation such as the nebular emission lines would be very valuable (see e.g. Krogager et al 2017). Here, only the Ly-α line is covered by our UVES spectrum.…”