We use 350 {mu}m angular diameter estimates from Planck to test the idea that some galaxies contain exceptionally cold (10-13 K) dust, since colder dust implies a lower surface brightness radiation field illuminating the dust, and hence a greater physical extent for a given luminosity. The galaxies identified from their spectral energy distributions as containing cold dust do indeed show the expected larger 350 {mu}m diameters. For a few cold dust galaxies where Herschel data are available, we are able to use submillimetre maps or surface brightness profiles to locate the cold dust, which as expected generally lies outside the optical galaxy.
We present new ^12^CO(1-0) observations of 59 late-type galaxies belonging to the Herschel Reference Survey (HRS), a complete K-band-selected, volume-limited (15<=D<=25Mpc) sample of nearby galaxies spanning a wide range in morphological type and luminosity. We studied different recipes to correct single-beam observations of nearby galaxies of different sizes and inclinations for aperture effects. This was done by comparing single-beam and multiple-beam observations along the major axis, which were corrected for aperture effects using different empirical or analytical prescriptions, to integrated maps of several nearby galaxies, including edge-on systems observed by different surveys. The resulting recipe is an analytical function determined by assuming that late-type galaxies are 3D exponentially declining discs with a characteristic scale length r_CO_=0.2r_24.5_, where r_24.5_ is the optical, g- (or B-) band isophotal radius at the 24.5mag/arcsec^2^ (25mag/arcsec^2^), as well as a scale height z_CO_=1/100r_24.5_. Our new CO data are then combined with those available in the literature to produce the most updated catalogue of CO observations for the HRS, now including 225 out of the 322 galaxies of the complete sample. The 3D exponential disc integration is applied to all the galaxies of the sample to measure their total CO fluxes, which are later transformed into molecular gas masses using a constant and a luminosity-dependent X_CO_ conversion factor. We also collect HI data for 315 HRS galaxies from the literature and present it in a homogenised form.
We are conducting COLD GASS, a legacy survey for molecular gas in nearby galaxies. Using the IRAM 30-m telescope, we measure the CO(1-0) line in a sample of ~350 nearby (D_I_~=100-200Mpc), massive galaxies (log(M*/M_{sun}_)>10.0). The sample is selected purely according to stellar mass, and therefore provides an unbiased view of molecular gas in these systems. By combining the IRAM data with Sloan Digital Sky Survey (SDSS) photometry and spectroscopy, GALEX imaging and high-quality Arecibo HI data, we investigate the partition of condensed baryons between stars, atomic gas and molecular gas in 0.1-10L* galaxies. In this paper, we present CO luminosities and molecular hydrogen masses for the first 222 galaxies. Description: To overcome this issue, the GALEX Arecibo SDSS Survey (GASS; Catinella et al. 2010, Cat. J/MNRAS/403/683) was designed to measure the neutral hydrogen content for a large, unbiased sample of ~1000 massive galaxies (M*>10^10^M_{sun}_), via longer pointed observations. GASS is a large programme currently under way at the Arecibo 305-m telescope, and is producing some of the first unbiased atomic gas scaling relations in the nearby Universe (Catinella et al. 2010, Cat. J/MNRAS/403/683; Schiminovich et al., 2010MNRAS.408..919S; Fabello et al., 2011MNRAS.411..993F). We are in the process of constructing a CO Legacy Data base for the GASS survey (COLD GASS), measuring the molecular gas content of a significant subsample of the GASS galaxies. We will then be able to quantify the link between atomic gas, molecular gas and stars in these systems.
We report results from a large molecular line survey of luminous infrared galaxies (LIRGs; L_IR_>~10^11^L_{sun}_) in the local Universe (z<=0.1), conducted during the last decade with the James Clerk Maxwell Telescope and the IRAM 30-m telescope. This work presents the CO and ^13^CO line data for 36 galaxies, further augmented by multi-J total CO line luminosities available for other infrared (IR) bright galaxies from the literature. This yields a combined sample of N=70 galaxies with the star formation (SF) powered fraction of their IR luminosities spanning L^(*)^IR_~10^10^-2x10^12^)L_{sun}_ and a wide range of morphologies.
After new observations of 39 galaxies at z=0.6-1.0 obtained at the IRAM 30m telescope, we present our full CO line survey covering the redshift range 0.2<z<1. Our aim is to determine the driving factors accounting for the steep decline in the star formation rate during this epoch. We study both the gas fraction, defined as Mgas/(Mgas+Mstar), and the star formation efficiency (SFE) defined by the ratio between far-infrared luminosity and molecular gas mass (L_FIR_/M(H_2_), i.e. a measure for the inverse of the gas depletion time. The sources are selected to be ultra-luminous infrared galaxies (ULIRGs), with L_FIR_ greater than 10^12^L_{sun}_, and experiencing starbursts. When we adopt a standard ULIRG CO-to-H_2_ conversion factor, their molecular gas depletion time is less than 100Myr. Our full survey has now filled the gap of CO observations in the 0.2<z<1 range covering almost half of cosmic history. The detection rate in the 0.6<z<1 interval is 38% (15 galaxies out of 39), compared to 60% for the 0.2<z<0.6 interval. The average CO luminosity is L'_CO_=1.8x10^10^K.km/s.pc^2^, corresponding to an average H_2_ mass of 1.45x10^10^M_{sun}_. From observation of 7 galaxies in both CO(2-1) and CO(4-3), a high gas excitation has been derived; together with the dust mass estimation, this supports the choice of our low ULIRG conversion factor between CO luminosity and H_2_ for our sample sources. We find that both the gas fraction and the SFE significantly increase with redshift, by factors of 3+/-1 from z=0 to 1, and therefore both quantities play an important role and complement each other in cosmic star formation evolution.
We present a catalog and imaging atlas of classical (collisional) RING galaxies distilled from the Arp-Madore Atlas of Southern Peculiar Galaxies and Associations and supplemented with other known RING galaxies from the published literature. The catalog lists the original host object, compiles available redshifts, and presents newly determined positions for the central (target) galaxy and its nearest companion(s). 127 collisional RING systems are illustrated and their components identified. All of the RINGS have plausible colliders identified; many are radial-velocity confirmed companions. Finally, we make note of the existence of a rare subclass of RING galaxies exemplified by AM 2136-492, double/concentric RING galaxies. These objects are predicted by numerical simulations, but they appear to be quite rare and/or short lived in nature.
In order to understand the past merging history of elliptical galaxies, we studied the optical-near-infrared (NIR) color gradients of 204 elliptical galaxies. These galaxies are selected from the overlap region of the Sloan Digital Sky Survey (SDSS) Stripe 82 and the UKIRT Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS). The use of optical and NIR data (g, r, and K) provides large wavelength baselines, and breaks the age-metallicity degeneracy, allowing us to derive age and metallicity gradients. The use of the deep SDSS Stripe 82 images makes it possible for us to examine how the color/age/metallicity gradients are related to merging features. We find that the optical-NIR color and the age/metallicity gradients of elliptical galaxies with tidal features are consistent with those of relaxed ellipticals, suggesting that the two populations underwent a similar merging history on average and that mixing of stars was more or less completed before the tidal features disappeared. Elliptical galaxies with dust features have steeper color gradients than the other two types, even after masking out dust features during the analysis, which can be due to a process involving wet merging. More importantly, we find that the scatter in the color/age/metallicity gradients of the relaxed and merging feature types decreases as their luminosities (or masses) increase at M>10^11.4^M_{sun}_ but stays large at lower luminosities. Mean metallicity gradients appear nearly constant over the explored mass range, but a possible flattening is observed at the massive end.
In this paper, we present a set of photometric observations in 15 colors of stars in the Landolt SA95 field with the BATC (Beijing-Arizona-Taipei-Connecticut) system. The wavelengths covered by the system range from 300nm to 1000nm. Visual magnitudes of the stars studied in the field are from the 10th to 20th mag. The observational methodology and the data reduction procedures are described. The relationships between the BATC intermediate-band system and the Landolt UBVRI broad band system are obtained. A catalogue of the photometry has been produced which contains the spectral energy distributions (SEDs) of 3613 stars.
We extend color-magnitude relations for moderate-luminosity X-ray active galactic nucleus (AGN) hosts and non-AGN galaxies through the galaxy formation epoch (z~1-4) in the Chandra Deep Field-North and Chandra Deep Field-South (CDF-N and CDF-S, respectively; jointly CDFs) surveys. This study was enabled by the deepest available X-ray data from the 2Ms CDF surveys as well as complementary ultradeep multiwavelength data in these regions. We utilized analyses of color-magnitude diagrams (CMDs) to assess the role of moderate-luminosity AGNs in galaxy evolution.
We here propose a new photometric technique to probe the possible nonlinear nature of globular clusters (GCs) color-metallicity relations (CMRs). In essence, a color distribution of GCs is a "projected" distribution of their metallicities. Since the form of CMRs hinges on which color is used, the shape of color distributions varies depending significantly on the colors. Among other optical colors, the u-band related colors (e.g., u-g and u-z) are theoretically predicted to exhibit significantly less inflected CMRs than other preferred CMRs (e.g., for g-z). As a case study, we performed the Hubble Space Telescope (HST)/WFPC2 archival u-band photometry for the M87 (NGC 4486) GC system with confirmed color bimodality. We show that the u-band color distributions are significantly different from that of g-z and consistent with our model predictions. With more u-band measurements, this method will support or rule out the nonlinear CMR scenario for the origin of GC color bimodality with high confidence.
