1 INAFOsservatorio Astronomico di Padova, Italy 2 University of Nottingham, UK 3 Ecole Polytechni... more 1 INAFOsservatorio Astronomico di Padova, Italy 2 University of Nottingham, UK 3 Ecole Polytechnique Federale de Lausanne, Switzerland 4 Institute for Astronomy, Edimburgh, UK 5 Ohio University, Athens, USA 6 University of Washington, Seattle, USA 7 INAFOsservatorio ...
Monthly Notices of the Royal Astronomical Society, 2014
ABSTRACT We present a catalogue and images of visually detected features, such as asymmetries, ex... more ABSTRACT We present a catalogue and images of visually detected features, such as asymmetries, extensions, warps, shells, tidal tails, polar rings, and obvious signs of mergers or interactions, in the faint outer regions (at and outside of R25) of nearby galaxies. This catalogue can be used in future quantitative studies that examine galaxy evolution due to internal and external factors. We are able to reliably detect outer region features down to a brightness level of 0.03 MJy sr−1 pixel−1 at 3.6 μm in the Spitzer Survey of Stellar Structure in Galaxies (S4G). We also tabulate companion galaxies. We find asymmetries in the outer isophotes in 22 ± 1 per cent of the sample. The asymmetry fraction does not correlate with galaxy classification as an interacting galaxy or merger remnant, or with the presence of companions. We also compare the detected features to similar features in galaxies taken from cosmological zoom re-simulations. The simulated images have a higher fraction (33 per cent) of outer disc asymmetries, which may be due to selection effects and an uncertain star formation threshold in the models. The asymmetries may have either an internal (e.g. lopsidedness due to dark halo asymmetry) or external origin.
ABSTRACT We obtained GALEX FUV, NUV, and Spitzer/IRAC 3.6$\mu$m photometry for > 2000 gala... more ABSTRACT We obtained GALEX FUV, NUV, and Spitzer/IRAC 3.6$\mu$m photometry for > 2000 galaxies, available for 90% of the S4G sample. We find a very tight "GALEX Blue Sequence (GBS)" in the (FUV-NUV) versus (NUV-[3.6]) color-color diagram which is populated by irregular and spiral galaxies, and is mainly driven by changes in the formation timescale ($\tau$) and a degeneracy between $\tau$ and dust reddening. The tightness of the GBS provides an unprecedented way of identifying star-forming galaxies and objects that are just evolving to (or from) what we call the "GALEX Green Valley (GGV)". At the red end of the GBS, at (NUV-[3.6]) > 5, we find a wider "GALEX Red Sequence (GRS)" mostly populated by E/S0 galaxies that has a perpendicular slope to that of the GBS and of the optical red sequence. We find no such dichotomy in terms of stellar mass (measured by $\rm{M}_{[3.6]}$), since both massive ($M_{\star} > 10^{11} M_{\odot}$) blue and red sequence galaxies are identified. The type that is proportionally more often found in the GGV are the S0-Sa's and most of these are located in high-density environments. We discuss evolutionary models of galaxies that show a rapid transition from the blue to the red sequence on timescale of $10^{8}$years.
Galaxy clusters are the most massive quasi-equilibrium objects in the Universe and are the meetin... more Galaxy clusters are the most massive quasi-equilibrium objects in the Universe and are the meeting places of the cosmos. Their deep potential wells are dominated by unseen dark matter, but contain a cosmologically representative baryon fraction in the form of galaxies and intergalactic gas. These are trapped in a virialized state, with the gas heated to tens of millions of
We present the ESO Distant Cluster Survey (EDisCS), a survey of distant galaxy clusters between r... more We present the ESO Distant Cluster Survey (EDisCS), a survey of distant galaxy clusters between redshifts of z=0.4 and 0.8. Candidate clusters were chosen from among the brightest objects identified in the Las Campanas Distant Cluster Survey (LCDCS), half with estimated redshift zest ˜ 0.5 and half with zest ˜ 0.8. The sample of 20 clusters was confirmed using two-color
1 INAFOsservatorio Astronomico di Padova, Italy 2 University of Nottingham, UK 3 Ecole Polytechni... more 1 INAFOsservatorio Astronomico di Padova, Italy 2 University of Nottingham, UK 3 Ecole Polytechnique Federale de Lausanne, Switzerland 4 Institute for Astronomy, Edimburgh, UK 5 Ohio University, Athens, USA 6 University of Washington, Seattle, USA 7 INAFOsservatorio ...
Monthly Notices of the Royal Astronomical Society, 2014
ABSTRACT We present a catalogue and images of visually detected features, such as asymmetries, ex... more ABSTRACT We present a catalogue and images of visually detected features, such as asymmetries, extensions, warps, shells, tidal tails, polar rings, and obvious signs of mergers or interactions, in the faint outer regions (at and outside of R25) of nearby galaxies. This catalogue can be used in future quantitative studies that examine galaxy evolution due to internal and external factors. We are able to reliably detect outer region features down to a brightness level of 0.03 MJy sr−1 pixel−1 at 3.6 μm in the Spitzer Survey of Stellar Structure in Galaxies (S4G). We also tabulate companion galaxies. We find asymmetries in the outer isophotes in 22 ± 1 per cent of the sample. The asymmetry fraction does not correlate with galaxy classification as an interacting galaxy or merger remnant, or with the presence of companions. We also compare the detected features to similar features in galaxies taken from cosmological zoom re-simulations. The simulated images have a higher fraction (33 per cent) of outer disc asymmetries, which may be due to selection effects and an uncertain star formation threshold in the models. The asymmetries may have either an internal (e.g. lopsidedness due to dark halo asymmetry) or external origin.
ABSTRACT We obtained GALEX FUV, NUV, and Spitzer/IRAC 3.6$\mu$m photometry for > 2000 gala... more ABSTRACT We obtained GALEX FUV, NUV, and Spitzer/IRAC 3.6$\mu$m photometry for > 2000 galaxies, available for 90% of the S4G sample. We find a very tight "GALEX Blue Sequence (GBS)" in the (FUV-NUV) versus (NUV-[3.6]) color-color diagram which is populated by irregular and spiral galaxies, and is mainly driven by changes in the formation timescale ($\tau$) and a degeneracy between $\tau$ and dust reddening. The tightness of the GBS provides an unprecedented way of identifying star-forming galaxies and objects that are just evolving to (or from) what we call the "GALEX Green Valley (GGV)". At the red end of the GBS, at (NUV-[3.6]) > 5, we find a wider "GALEX Red Sequence (GRS)" mostly populated by E/S0 galaxies that has a perpendicular slope to that of the GBS and of the optical red sequence. We find no such dichotomy in terms of stellar mass (measured by $\rm{M}_{[3.6]}$), since both massive ($M_{\star} > 10^{11} M_{\odot}$) blue and red sequence galaxies are identified. The type that is proportionally more often found in the GGV are the S0-Sa's and most of these are located in high-density environments. We discuss evolutionary models of galaxies that show a rapid transition from the blue to the red sequence on timescale of $10^{8}$years.
Galaxy clusters are the most massive quasi-equilibrium objects in the Universe and are the meetin... more Galaxy clusters are the most massive quasi-equilibrium objects in the Universe and are the meeting places of the cosmos. Their deep potential wells are dominated by unseen dark matter, but contain a cosmologically representative baryon fraction in the form of galaxies and intergalactic gas. These are trapped in a virialized state, with the gas heated to tens of millions of
We present the ESO Distant Cluster Survey (EDisCS), a survey of distant galaxy clusters between r... more We present the ESO Distant Cluster Survey (EDisCS), a survey of distant galaxy clusters between redshifts of z=0.4 and 0.8. Candidate clusters were chosen from among the brightest objects identified in the Las Campanas Distant Cluster Survey (LCDCS), half with estimated redshift zest ˜ 0.5 and half with zest ˜ 0.8. The sample of 20 clusters was confirmed using two-color
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Papers by Dennis Zaritsky