A molecular hydrogen absorber at a lookback time of 12.4 billion years, corresponding to 10$%$ of the age of the universe today, is analyzed to put a constraint on a varying proton--electron mass ratio, $mu$. A high resolution spectrum of the J1443$+
$2724 quasar, which was observed with the Very Large Telescope, is used to create an accurate model of 89 Lyman and Werner band transitions whose relative frequencies are sensitive to $mu$, yielding a limit on the relative deviation from the current laboratory value of $Deltamu/mu=(-9.5pm5.4_{textrm{stat}} pm 5.3_{textrm{sys}})times 10^{-6}$.
We present a new `supercalibration technique for measuring systematic distortions in the wavelength scales of high resolution spectrographs. By comparing spectra of `solar twin stars or asteroids with a reference laboratory solar spectrum, distortion
s in the standard thorium--argon calibration can be tracked with $sim$10 m s$^{-1}$ precision over the entire optical wavelength range on scales of both echelle orders ($sim$50--100 AA) and entire spectrographs arms ($sim$1000--3000 AA). Using archival spectra from the past 20 years we have probed the supercalibration history of the VLT--UVES and Keck--HIRES spectrographs. We find that systematic errors in their wavelength scales are ubiquitous and substantial, with long-range distortions varying between typically $pm$200 m s$^{-1}$ per 1000 AA. We apply a simple model of these distortions to simulated spectra that characterize the large UVES and HIRES quasar samples which previously indicated possible evidence for cosmological variations in the fine-structure constant, $alpha$. The spurious deviations in $alpha$ produced by the model closely match important aspects of the VLT--UVES quasar results at all redshifts and partially explain the HIRES results, though not self-consistently at all redshifts. That is, the apparent ubiquity, size and general characteristics of the distortions are capable of significantly weakening the evidence for variations in $alpha$ from quasar absorption lines.
Large statistical samples of quasar spectra have previously indicated possible cosmological variations in the fine-structure constant, $alpha$. A smaller sample of higher signal-to-noise ratio spectra, with dedicated calibration, would allow a detail
ed test of this evidence. Towards that end, we observed equatorial quasar HS 1549$+$1919 with three telescopes: the Very Large Telescope, Keck and, for the first time in such analyses, Subaru. By directly comparing these spectra to each other, and by `supercalibrating them using asteroid and iodine-cell tests, we detected and removed long-range distortions of the quasar spectras wavelength scales which would have caused significant systematic errors in our $alpha$ measurements. For each telescope we measure the relative deviation in $alpha$ from the current laboratory value, $Deltaalpha/alpha$, in 3 absorption systems at redshifts $z_{mathrm{abs}}=1.143$, 1.342, and 1.802. The nine measurements of $Deltaalpha/alpha$ are all consistent with zero at the 2-$sigma$ level, with 1-$sigma$ statistical (systematic) uncertainties 5.6--24 (1.8--7.0) parts per million (ppm). They are also consistent with each other at the 1-$sigma$ level, allowing us to form a combined value for each telescope and, finally, a single value for this line of sight: $Deltaalpha/alpha=-5.4 pm 3.3_{mathrm{stat}} pm 1.5_{mathrm{sys}}$ ppm, consistent with both zero and previous, large samples. We also average all Large Programme results measuring $Deltaalpha/alpha=-0.6 pm 1.9_{mathrm{stat}} pm 0.9_{mathrm{sys}}$ ppm. Our results demonstrate the robustness and reliability at the 3 ppm level afforded by supercalibration techniques and direct comparison of spectra from different telescopes.
Galaxies are thought to be fed by the continuous accretion of intergalactic gas, but direct observational evidence has been elusive. The accreted gas is expected to orbit about the galaxys halo, delivering not just fuel for star-formation but also an
gular momentum to the galaxy, leading to distinct kinematic signatures. Here we report observations showing these distinct signatures near a typical distant star-forming galaxy where the gas is detected using a background quasar passing 26 kpc from the host. Our observations indicate that gas accretion plays a major role in galaxy growth since the estimated accretion rate is comparable to the star-formation rate.
[Abridged] In order to understand which process (e.g. galactic winds, cold accretion) is responsible for the cool (T~10^4 K) halo gas around galaxies, we embarked on a program to study the star-formation properties of galaxies selected by their MgII
absorption signature in quasar spectra. Specifically, we searched for the H-alpha line emission from galaxies near very strong z=2 MgII absorbers (with rest-frame equivalent width EW>2 AA) because these could be the sign-posts of outflows or inflows. Surprisingly, we detect H-alpha from only 4 hosts out of 20 sight-lines (and 2 out of the 19 HI-selected sight-lines), despite reaching a star-formation rate (SFR) sensitivity limit of 2.9 M/yr (5-sigma) for a Chabrier initial mass function. This low success rate is in contrast with our z=1 survey where we detected 66% (14/21) of the MgII hosts. Taking into account the difference in sensitivity between the two surveys, we should have been able to detect >11.4 of the 20 z=2 hosts whereas we found only 4 galaxies. Interestingly, all the z=2 detected hosts have observed SFR greater than 9 M/yr, well above our sensitivity limit, while at z=1 they all have SFR less than 9 M/yr, an evolution that is in good agreement with the evolution of the SFR main sequence. Moreover, we show that the z=2 undetected hosts are not hidden under the quasar continuum after stacking our data and that they also cannot be outside our surveyed area. Hence, strong MgII absorbers could trace star-formation driven winds in low-mass halos (Mhalo < 10^{10.6} Msun). Alternatively, our results imply that z=2 galaxies traced by strong MgII absorbers do not form stars at a rate expected (3--10 M/yr) for their (halo or stellar) masses, supporting the existence of a transition in accretion efficiency at Mhalo ~ 10^{11} Msun. This scenario can explain both the detections and the non-detections.
(Abridged) We performed a spectroscopic galaxy survey, complete to m<20.3 (L_B>0.15L_B* at z=0.3), within 100x100 of the quasar Q1127-145 (z=1.18). The VLT/UVES quasar spectrum contains three z<0.33 MgII absorption systems. We obtained eight new gala
xy redshifts, adding to the four previously known, and galaxy star formation rates and metallicities were computed where possible. A strong MgII system [W_r(2796)=1.8A], which is a known DLA, had three previously identified galaxies; we found two additional galaxies associated with this system. These five galaxies form a group with diverse properties, such as a luminosity range of 0.04<L_B<0.63L_B*, an impact parameter range of 17<D<241kpc and velocity dispersion of 115km/s. The DLA group galaxy redshifts span beyond the 350km/s velocity spread of the metallic absorption lines of the DLA itself. The two brightest group galaxies have SFRs of a few Msun/yr and should not have strong winds. We have sufficient spectroscopic information to directly compare three of the five group galaxies (emission-line) metallicities with the DLA (absorption) metallicity: the DLA metallicity is 1/10th solar, substantially lower than the three galaxies which range between less than 1/2 solar to solar metallicity. HST/WFPC-2 imaging shows perturbed morphologies for the three brightest group galaxies, with tidal tails extending 25kpc. We favor a scenario where the DLA absorption originates from tidal debris in the group environment. Another absorber exhibits weak MgII absorption [W_r(2796)=0.03A] and had a previously identified galaxy at a similar redshift. We have identified a second galaxy associated with this system. Both galaxies have solar metallicities and unperturbed morphologies. The SFR of one galaxy is much lower than expected for strong outflows. Finally, we have identified five galaxies at large impact parameters with no associated MgII absorption.
Recent studies of the circumgalactic gaseous environment of the Milky Way have concentrated on the distribution, chemical composition, and physical properties of the most massive neutral gas clouds and the highly-ionized halo absorbers. Relatively li
ttle effort has been put so far in exploring the circumgalactic neutral and weakly ionized metal absorbers at low HI column densities. With our work we systematically study the distribution and physical properties of neutral and ionised low-column density gas in the halo of the Milky Way. We combine CaII and NaI absorption line measurements with HI 21-cm emission line data. For some of the sight lines high-resolution radio synthesis observations were performed allowing us to study small-scale structures that cannot be resolved with single dish telescopes. In total 177 lines of sight were observed, providing a large absorption-selected data sample for the analysis of IVC and HVC gas in the circumgalactic environment of the Milky Way. The study allows us to compare the observed absorption column density distribution (CDD) of gas in the Milky Way halo with the overall CDD of intervening absorbers towards quasars. The sensitive absorption line analysis enables us to identify the neutral and ionised gaseous structures at low column densities and small angular extent that possibly remain unseen in large 21-cm all-sky surveys. If this gas cover a significant portion of the sky, it possibly has a large influence on the evolution of the Milky Way.
