Search

We identify and characterize compact dwarf starburst (CDS) galaxies in the RESOLVE survey, a volume-limited census of galaxies in the local universe, to probe whether this population contains any residual ``blue nuggets,'' a class of intensely star-forming compact galaxies first identified at high redshift $z$. Our 50 low-$z$ CDS galaxies are defined by dwarf masses (stellar mass $M_* < 10^{9.5}$ M$_{\odot}$), compact bulged-disk or spheroid-dominated morphologies (using a quantitative criterion, $��_��> 8.6$), and specific star formation rates above the defining threshold for high-$z$ blue nuggets ($\log$ SSFR [Gyr$^{-1}] > -0.5$). Across redshifts, blue nuggets exhibit three defining properties: compactness relative to contemporaneous galaxies, abundant cold gas, and formation via compaction in mergers or colliding streams. Those with halo mass below $M_{\rm halo} \sim 10^{11.5}$ M$_{\odot}$ may in theory evade permanent quenching and cyclically refuel until the present day. Selected only for compactness and starburst activity, our CDS galaxies generally have $M_{\rm halo} \lesssim 10^{11.5}$ M$_{\odot}$ and gas-to-stellar mass ratio $\gtrsim$1. Moreover, analysis of archival DECaLS photometry and new 3D spectroscopic observations for CDS galaxies reveals a high rate of photometric and kinematic disturbances suggestive of dwarf mergers. The SSFRs, surface mass densities, and number counts of CDS galaxies are compatible with theoretical and observational expectations for redshift evolution in blue nuggets. We argue that CDS galaxies represent a maximally-starbursting subset of traditional compact dwarf classes such as blue compact dwarfs and blue E/S0s. We conclude that CDS galaxies represent a low-$z$ tail of the blue nugget phenomenon formed via a moderated compaction channel that leaves open the possibility of disk regrowth and evolution into normal disk galaxies., 22 pages, 13 figures. Accepted for publication in MNRAS

et al., We present Hubble Space Telescope WFC3-IR imaging in the fields of six apparently bright dusty star-forming galaxies (DSFGs) at z = 2-4 identified by their rest-frame far-infrared colors using the Planck and Herschel space facilities. We detect near-infrared counterparts for all six submillimeter sources, allowing us to undertake strong-lensing analyses. One field in particular stands out for its prominent giant arcs, PLCK G165.7+67.0 (G165). After combining the color and morphological information, we identify 11 sets of image multiplicities in this one field. We construct a strong-lensing model constrained by this lensing evidence, which uncovers a bimodal spatial mass distribution, and from which we measure a mass of (2.6 ± 0.11) × 1014 M ⊙ within ~250 kpc. The bright (S 350 ≈ 750 mJy) DSFG appears as two images: a giant arc with a spatial extent of that is merging with the critical curve, and a lower-magnification counterimage that is detected in our new longer-wavelength ground- and space-based imaging data. Using our ground-based spectroscopy, we calculate a dynamical mass of ${1.3}_{-0.70}^{+0.04}\times {10}^{15}$ M ⊙ to the same fixed radius, although this value may be inflated relative to the true value if the velocity distribution is enhanced in the line-of-sight direction. We suggest that the bimodal mass taken in combination with the weak X-ray flux and low SZ decrement may be explained as a pre-merger for which the intracluster gas is diluted along the line of sight, while the integrated surface mass density is supercritical to strong-lensing effects., J.M.D. acknowledges the support of project AYA2015-64508-P (MINECO/FEDER, UE).

Public data from the 2dF quasar survey (2QZ) and 2dF/SDSS LRG & QSO (2SLAQ), with their vast reservoirs of spectroscopically located and identified sources, afford us the chance to more accurately study their real space correlations in the hopes of identifying the physical processes that trigger quasar activity. We have used these two public databases to measure the projected cross correlation, $\omega_p$, between quasars and luminous red galaxies. We find the projected two-point correlation to have a fitted clustering radius of $r_0, = 5.3 \pm 0.6 $ and a slope, $\gamma =1.83 \pm 0.42 $ on scales from 0.7-27$h^{-1}$Mpc. We attempt to understand this strong correlation by separating the LRG sample into 2 populations of blue and red galaxies. We measure at the cross correlation with each population. We find that these quasars have a stronger correlation amplitude with the bluer, more recently starforming population in our sample than the redder passively evolving population, which has a correlation that is much more noisy and seems to flatten on scales $< 5h^{-1}$Mpc. We compare this result to published work on hierarchical models. The stronger correlation of bright quasars with LRGs that have undergone a recent burst of starformation suggests that the physical mechanisms that produce both activities are related and that minor mergers or tidal effects may be important triggers of bright quasar activity and/or that bright quasars are less highly biased than faint quasars., Comment: Accepted for publication in ApJ

We present the first sample of galaxy clusters selected on the basis of their weak gravitational lensing shear. The shear induced by a cluster is a function of its mass profile and its redshift relative to the background galaxies being sheared; in contrast to more traditional methods of selecting clusters, shear selection does not depend on the cluster's star formation history, baryon content, or dynamical state. Because mass is the property of clusters which provides constraints on cosmological parameters, the dependence on these other parameters could induce potentially important biases in traditionally-selected samples. Comparison of a shear-selected sample with optically and X-ray selected samples is therefore of great importance. Here we present the first step toward a new shear-selected sample: the selection of cluster candidates from the first 8.6 deg$^2$ of the 20 deg$^2$ Deep Lens Survey (DLS), and tabulation of their basic properties such as redshifts and optical and X-ray counterparts., Comment: v2 as published in ApJ, 45 pages, 18 figures. Biggest change from v1 is addition of a figure showing the 1-point distribution of pixels in the mass maps and control "mass maps" using the non-tangential component of shear, demonstrating that all candidate peaks are higher than any peak seen in the control maps

We report on the methodology and first results from the Deep Lens Survey transient search. We utilize image subtraction on survey data to yield all sources of optical variability down to 24th magnitude. Images are analyzed immediately after acquisition, at the telescope and in near-real time, to allow for followup in the case of time-critical events. All classes of transients are posted to the web upon detection. Our observing strategy allows sensitivity to variability over several decades in timescale. The DLS is the first survey to classify and report all types of photometric and astrometric variability detected, including solar system objects, variable stars, supernovae, and short timescale phenomena. Three unusual optical transient events were detected, flaring on thousand-second timescales. All three events were seen in the B passband, suggesting blue color indices for the phenomena. One event (OT 20020115) is determined to be from a flaring Galactic dwarf star of spectral type dM4. From the remaining two events, we find an overall rate of ��= 1.4 events deg-2 day-1 on thousand-second timescales, with a 95% confidence limit of ��< 4.3. One of these events (OT 20010326) originated from a compact precursor in the field of galaxy cluster Abell 1836, and its nature is uncertain. For the second (OT 20030305) we find strong evidence for an extended extragalactic host. A dearth of such events in the R passband yields an upper 95% confidence limit on short timescale astronomical variability between 19.5 < R < 23.4 of ��_R < 5.2. We report also on our ensemble of astrometrically variable objects, as well as an example of photometric variability with an undetected precursor., 24 pages, 12 figures, 3 tables. Accepted for publication in ApJ. Variability data available at http://dls.bell-labs.com/transients.html

This paper outlines an infrared spectroscopic technique to measure the radial velocities of faint secondaries in known single-lined binaries. The paper presents our H-band observations with the CSHELL and Phoenix spectrographs and describes detections of three low-mass secondaries in main-sequence binaries: G147-36, G164-67, and HD144284 with mass ratios of 0.562+-0.011, 0.423+-0.042, and 0.380+-0.013, respectively. The latter is one of the smallest mass ratios derived to date.

Modern time-domain surveys have demonstrated that finding variable objects is relatively straightforward. The problem now is one of selecting and following up discoveries. With even larger-scale surveys on the horizon, the magnitude of the problem will inevitably increase. One way to prepare for the coming deluge is to have realistic estimates of the numbers of potential detections so that resources can be developed to meet that need. To that end, astronomers at the National Optical Astronomy Observatory (NOAO) have begun a project to characterize the variable sky in terms of type of objects, distribution on the sky and range of variation.

Weak gravitational lensing by clusters and superclusters can change our perception of the distribution of bright background quasars through the phenomenon of magnification bias. It has been suggested that this lensing will lead to an association of moderate-redshift quasars (z ~ 1.0–2.0) and foreground galaxies (z ~ 0.2–0.3). We report on the analysis of a sample of 90 CCD fields centered on moderate-redshift quasars that are bright at both radio (S5 GHz > 1 Jy) and optical (V < 21.0) wavelengths, along with 12 control fields. The quasars presented here are chosen to have the highest potential for evidence of this weak lensing effect. We find no evidence for the presence of rich galaxy clusters (Abell richness class 1) in the foreground of these fields. However, using a Spearman rank-order correlation test, we detect a correlation between galaxy number density and angular distance from bright quasars on scales of ~15' with a significance of 96%. The observed correlation is unlikely the result of Galactic dust and is consistent with weak gravitational lensing of the quasars by foreground matter. We also determine the two-point angular correlation function between these background quasars and foreground galaxies. We find a correlation amplitude of 0.056 ± 0.020 over scales of ~5'. This angular correlation is consistent with the semianalytic weak gravitational lensing models of Dolag & Bartelmann (published in 1997), which incorporate nonlinear evolution of mass clustering.

We analyze Hubble Space Telescope/Goddard High Resolution Spectrograph spectra of AB Doradus, the prototypical, ultrarapidly rotating K dwarf. We observed chromospheric (Mg II) and transition-region (C II, Si IV, C IV, and N V) lines periodically throughout the stellar rotation period and provide a low-dispersion stellar atlas of 78 emission lines. The quiescent line profiles of the chromospheric and transition-region lines show narrow cores superposed on very broad wings. The broad wings of the Mg II k and h lines and of the transition-region lines can be explained by emission from gas corotating with the star and extending out to near the Keplerian corotation radius (2.8 stellar radii). While this is not a unique solution, it is consistent with previous studies of Hα emission, which are naturally explained by large corotating prominences. We find no evidence for rotational modulation of the emission-line fluxes. The density diagnostics suggest that the transition region is formed at constant pressure, with an electron density of 2–3 × 1012 cm-3 at a temperature of 3 × 104 K. The electron pressure is about 100 times larger than that for the quiet Sun. The emission-measure distribution shows a minimum between log T = 5 and 5.5. The Mg II line exhibits three interstellar absorption components along the 15 pc line of sight. We identify the lowest velocity component with the G Cloud, but the other components are not identified with any interstellar clouds previously detected from other lines of sight.

We find angular correlations between high redshift radio selected QSOs from the 1 Jy Catalog and APM galaxies on ~1 degree scales. We demonstrate that observed correlations are qualitatively consistant with a gravitational lensing explanation and are inconsistant with a Galactic dust obscuration model. Comparing our results with those of Benitez and Martinez-Gonzalez, who also use 1 Jy sources and APM galaxies we come to the conclusion that galaxy selection criteria can have a major effect on the angular scale and amplitude of detected correlations.

Using high resolution near-infrared spectroscopy with the Keck telescope, we have detected the radial velocity signatures of the cool secondary components in four optically identified pre-main-sequence, single-lined spectroscopic binaries. All are weak-lined T Tauri stars with well-defined center of mass velocities. The mass ratio for one young binary, NTTS 160905-1859, is M2/M1 = 0.18+/-0.01, the smallest yet measured dynamically for a pre-main-sequence spectroscopic binary. These new results demonstrate the power of infrared spectroscopy for the dynamical identification of cool secondaries. Visible light spectroscopy, to date, has not revealed any pre-main-sequence secondary stars with masses, Accepted for publication in the April, 2002, ApJ; 6 figures

Low-resolution UV observations of the bright, low-redshift BL Lac object PKS 2155-304 have been obtained by the HST's high-resolution spectrograph. Attention is here given to results on the number of intergalactic H I Ly-alpha components in the line-of-sight toward this object. The highest-redshift of the observed Ly-alpha systems furnishes a lower limit on the distance of the BL Lac object; this distance is consistent with the approximate redshift deduced from CCD imagery of the probable host galaxy for PKS 2155-304.