Kathy L. Cooksey

Metal-enriched, subkiloparsec gas clumps in the circumgalactic medium of a faint z = 2.5 galaxy

We report the serendipitous detection of a 0.2 L ,Ly emitting galaxy at redshift 2.5 at an impact parameter of 50 kpc from a bright background QSO sightline. A high-resolution spectrum of the QSO reveals a partial Lyman-limit absorption system (N HI = 10 16:94 0:10 cm 2 ) with many associated metal absorption lines at the same redshift as the foreground galaxy. Using photoionization models that carefully treat measurement errors and marginalise over uncertainties in the shape and normalisation of the ionizing radiation spectrum, we derive the total hydrogen column density NH = 10 19:4 0:3 cm 2 , and show that all the absorbing clouds are metal enriched, with Z = 0:1‐0:6 Z . These metallicities and the system’s large velocity width (436 kms 1 ) suggest the gas is produced by an outflowing wind. Using an expanding shell model we estimate a mass outflow rate of 5M yr 1 . Our photoionization model yields extremely small sizes (<100‐500 pc) for the absorbing clouds, which we argue is typical of high column density absorbers in the circumgalactic medium (CGM). Given these small sizes and extreme kinematics, it is unclear how the clumps survive in the CGM without being destroyed by hydrodynamic instabilities. The small cloud sizes imply that even state-of-the-art cosmological simulations require more than a 1000-fold improvement in mass resolution to resolve the hydrodynamics relevant for cool gas in the CGM.

CHARACTERIZING THE LOW-REDSHIFT INTERGALACTIC MEDIUM TOWARD PKS 1302-102

We present a detailed analysis of the intergalactic metal-line absorption systems in the archival HST STIS and FUSE ultraviolet spectra of the low-redshift quasar PKS 1302?102 ( -->zQSO = 0.2784). We supplement the archive data with CLOUDY ionization models and a survey of galaxies in the quasar field. There are 15 strong Ly? absorbers with column densities --> NH I > 14. Of these, six are associated with at least C III ?977 absorption [ -->log N(C+ +) > 13]; this implies a redshift density --> dNC III/dz = 36-9+13 (68% confidence limits) for the five detections with rest equivalent width -->Wr > 50 m?. Two systems show O VI ??1031, 1037 absorption in addition to C III [ -->log N(O+ 5) > 14]. One is a partial Lyman limit system (--> log NH I = 17) with associated C III, O VI, and Si III ?1206 absorption. There are three tentative O VI systems that do not have C III detected. For one O VI doublet with both lines detected at 3 ? with -->Wr > 50 m?, --> dNO VI/dz = 7-4+9. We also search for O VI doublets without Ly? absorption but identify none. From CLOUDY modeling, these metal-line systems have metallicities spanning the range ? -->4 [ M/H ] ? 0.3. The two O VI systems with associated C III absorption cannot be single-phase, collisionally ionized media based on the relative abundances of the metals and kinematic arguments. From the galaxy survey, we discover that the absorption systems are in a diverse set of galactic environments. Each metal-line system has at least one galaxy within 500 km s?1 and 600 -->h?175 kpc with -->L > 0.1L*.

Multi-wavelength observations of the star forming region in L1616

We present the results of a multi-wavelength study of the star forming region in L1616. Our observations include ROSAT All-Sky Survey (RASS) and High Resolution Imager (HRI) X-ray observations, optical wide-field imaging and near-IR imaging data and optical long-slit and multi-object spectroscopic follow-up. 22 new low-mass pre-main sequence (PMS) stars are found to be distributed mainly to the East of the L1616 cometary cloud, in about a one-square-degree field. We find that the class-III infrared sources outnumber the class-II infrared sources by a factor of about three. The X-ray properties of the PMS stars in L1616 are quite similar to those of PMS stars detected in the Orion Nebula Cluster. The comparison of the position of the L1616 PMS stars in the HR diagram with theoretical PMS evolutionary tracks yields an average age of 1–2 Myr, with a very small age spread of about 1 Myr. Unlike the fossil star forming regions in Orion, L1616 appears to be a region of on-going star formation relatively far from the Orion A and B clouds. Given the small age spread, the spatial distribution of the PMS stars relative to the head of the cloud, as well as its cometary shape and high star formation efficiency, we conclude that the star formation in L1616 was most likely induced by a single event, the impact of the winds of the massive stars of the Orion OB association or a supernova explosion being the possible triggers. The Initial Mass Function (IMF) in L1616 is roughly consistent with that of the field in the mass range 0.3 < M/M_⊙ < 2.5. Several faint objects, detected in our optical images, are good candidates for young Brown Dwarfs (BDs). We might expect the number of BDs in L1616 to be intermediate between Taurus and the Trapezium.

Andromeda’s Parachute: A Bright Quadruply Lensed Quasar at z = 2.377

We present Keck Cosmic Web Imager spectroscopy of the four putative images of the lensed quasar candidate J014709+463037 recently discovered by Berghea et al. (2017). The data verify the source as a quadruply lensed, broad absorption-line quasar having z_S = 2.377 +/- 0.007. We detect intervening absorption in the FeII 2586, 2600, MgII 2796, 2803, and/or CIV 1548, 1550 transitions in eight foreground systems, three of which have redshifts consistent with the photometric-redshift estimate reported for the lensing galaxy (z_L ~ 0.57). By virtue of their positions on the sky, the source images probe these absorbers over transverse physical scales of ~0.3-21 kpc, permitting assessment of the variation in metal-line equivalent width W_r as a function of sight-line separation. We measure differences in W_r,2796 of 50% over the same scales across the majority of sight-line pairs, while CIV absorption exhibits a wide range in W_r,1548 differences of ~5-80% within transverse distances less than ~3 kpc. J014709+463037 is one of only a handful of z > 2 quadruply lensed systems for which all four source images are very bright (r = 15.4-17.7 mag) and are easily separated in ground-based seeing conditions. As such, it is an ideal candidate for higher-resolution spectroscopy probing the spatial variation in the kinematic structure and physical state of intervening absorbers.

The COS CGM Compendium. I. Survey Design and Initial Results

We present a neutral hydrogen-selected absorption-line survey of gas with HI column densities 15 2 orders of magnitude at any given N(HI), indicating a wide range of metallicities (from solar to <1/100 solar). In the range 16.2<log N(HI)<17, there is a gap in the N(MgII) distribution corresponding to gas with ~10% solar metallicity, consistent with the gap seen in the previously identified bimodal metallicity distribution in this column density regime. Less than 3% of the absorbers in our sample show no detectable metal absorption, implying truly-pristine gas at z<1 is uncommon. We find [FeII/MgII] = -0.4+/-0.3, and since alpha-enhancement can affect this ratio, dust depletion is extremely mild.

FUV Observations of a Strong OVI Absorber and a Lyman Limit System

The O VI absorber at z = 0.2028 detected in the spectrum of the QSO PKS 0312–77 is the strongest discovered so far in the low redshift Universe (logN(OVI) = 14.95±0.05,) and is observed near a Lyman limit system (LLS). We present an analysis of these absorbers and their connection to galaxies based on a combination of FUV and NUV spectra of PKS 0312–77 obtained from FUSE and HST/STIS E140M/E230M and optical imaging and spectroscopy of galaxies in the field. Based on O I/H I and a photoionization model, we find a metallicity of 0.25 solar for the LLS, too enriched to be pristine IGM gas. We find that the gas resulting from the merger of a 0.7L* galaxy (impact parameter of 38 kpc) is the likely origin for the LLS. At −190 km/s from the LLS, another absorber is found with a supersolar metallicity. Outflow from this galaxy is likely responsible for this supersolar, fully ionized absorber. The metallicity variation is a possible evidence for poor mixing of metals on galactic structure as observed in the Milky ...