The Unresolved Galaxies with Gaia

EAS Publications Series, 2002

The Astronomical Journal, 2008

We present a revaluation of the optical morphology for 549 galaxies from the Catalog of Isolated Galaxies in the Northern Hemisphere (CIG; Karachentseva 1973) that are available in the Sloan Digital Sky Survey (SDSS; DR6). Both the high resolution and high dynamic range of the SDSS images and our semi-automatic image processing scheme, allow for a major quality and uniform morphological analysis. The processing scheme includes (1) sky-subtracted, cleaned, and logarithmic scaled g−band images; (2) filtered-enhanced versions of the images in (1); and (3) the corresponding RGB images available in the SDSS database. Special attention was paid for distinguishing between E, S0, and Sa candidates through an additional analysis of (4) the surface brightness, ǫ, P A and A 4 /B 4 Fourier series expansion profiles. An atlas of mosaics containing [(1), (2) and (3)] images for Sab-Sm/Irr types and [(1), (2), (3), (4)] images for E/S0/Sa types was produced and is available on the web. The median type in the sample corresponds to Sbc, with 65% of the sample being of this type or later. A scarce population of E (3.5%) and S0 (5%) galaxies amounting to 8.5%, and a non-negligible 14% fraction of early-type SaSab spirals are identified. We compare our results against a previous reclassification of the CIG catalog based on the digitized POSS II images (Sulentic et al. 2006). We calculate also the gri absolute magnitudes corrected by Galactic and internal extinctions and present the g − i color distribution and the color-magnitude diagram. Among the spirals, we find tentative fractions of strong and suspected bars of 65.8% and of 33.3% of rings. A detailed image analysis of the E galaxies (18) allows us to find a richness of distinct substructure in their isophotal shape and also of morphological distortions. At least 78% of the E galaxies show some kind of morphological distortion (shells, dust lanes, diffuse halos, etc.), suggesting that these galaxies suffered late dry mergers. The isophotes of 42% (37%) of the E galaxies are boxy (disky). Among 4 blue E's, 3 are disky. Finally, we calculate for all the sample the CAS (concentration, asymmetry and clumpiness) structural parameters in the ugriz bands. We analyze the loci of these galaxies in different projections of the CAS volume diagram and discuss some trends of the CAS parameters with the color band, as well as with the morphological type and the galaxy color.

The Astronomical …, 2001

We study the optical colors of 147,920 galaxies brighter than g * = 21, observed in five bands by the Sloan Digital Sky Survey (SDSS) over ∼100 2 • of high Galactic latitude sky along the Celestial Equator. The distribution of galaxies in the g * − r * vs. u * − g * color-color diagram is strongly bimodal, with an optimal color separator of u * − r * = 2.22. We use visual morphology and spectral classification of subsamples of 287 and 500 galaxies respectively, to show that the two peaks correspond roughly to early (E, S0, Sa) and late (Sb, Sc, Irr) type galaxies, as expected from their different stellar populations. We also find that the colors of galaxies are correlated with their radial profiles, as measured by the concentration index and by the likelihoods of exponential and de Vaucouleurs' profile fits. While it is well known that late type galaxies are bluer than early type galaxies, this is the first detection of a local minimum in their color distribution. In all SDSS bands, the counts vs. apparent magnitude relations for the two color types are significantly different, and demonstrate that the fraction of blue galaxies increases towards the faint end.

We present a catalogue of morphologically classified bright galaxies in the north equatorial stripe (230 deg 2 ) derived from the Third Data Release of the Sloan Digital Sky Survey (SDSS). Morphological classification is performed by visual inspection of images in the g band. The catalogue contains 2253 galaxies complete to a magnitude limit of r = 16 after Galactic extinction correction, selected from 2658 objects that are judged as extended in the photometric catalogue in the same magnitude limit. 1866 galaxies in our catalogue have spectroscopic information. A brief statistical analysis is presented for the frequency of morphological types and mean colours in the catalogue. A visual inspection of the images reveals that the rate of interacting galaxies in the local Universe is approximately 1.5% in the r ≤ 16 sample. A verification is made for the photometric catalogue generated by the SDSS, especially as to its bright end completeness.

Open Astronomy

We study the morphological distribution of galaxies in some nearby clusters, using the Sloan Digital Sky Survey – Data Release 9 (SDSS-DR9). The segregation between early-type galaxies and late-type ones is investigated in g – r / u – g color space, using the color cut u – r = 2.22. The results are compared with those obtained using a color cut that changes with magnitude. They are found to be consistent, particularly for late-type galaxies. The results obtained by the fixed color-cut criterion are also found to be consistent with those obtained by the inverse concentration index parameter, especially for early-type galaxies. Comparable results are obtained for the stacked sample, whose morphologies, given by the fixed color-cut criterion are compared with the visual morphologies provided by the Galaxy Zoo project. A good degree of consistency is seen, which becomes more evident for late-type galaxies.

Astronomy & Astrophysics, 2014

Aims. Besides its major objective tuned to detecting the stellar galactic population, the Gaia mission experiment will also observe a large number of galaxies. In this work we intend to evaluate the number and the characteristics of the galaxies that will effectively pass the on-board selection algorithm of Gaia. Methods. The detection of objects in Gaia will be performed in a section of the focal plane known as the Sky Mapper. Considering the Video Processing Algorithm criterion of detection and the known light profiles of disc and bulges galaxies, we assess the number and the type of extra-galactic objects that will be observed by Gaia. Results. We show that the stellar disc population of galaxies will be very difficult to observe. In contrast, the spheroidal component of elliptical galaxies and bulges having higher central surface brightness and steeper brightness profile will be easier to detect. We estimate that most of the 20 000 elliptical population of nearby galaxies inside the local region up to 170 Mpc are in a state to be observed by Gaia. A similar number of bulges could also be observed, although the low luminosity bulges should escape detection. About two thirds of the more distant objects up to 600 Mpc could also be detected, increasing the total sample to half a million objects including ellipticals and bulges. The angular size of the detected objects will never exceed 4.72 arcsec, which is the size of the largest transmitted windows. Conclusions. A heterogeneous population of elliptical galaxies and bulges will be observable by Gaia. This nearby Universe sample of galaxies should constitute a very rich and interesting sample for studying their structural properties and their distribution.

Monthly Notices of the Royal Astronomical Society, 2008

We perform a detailed photometric analysis (bulge-disk-bar decomposition and Concentration-Asymmetry-Clumpiness -CAS parametrization) for a well defined sample of isolated galaxies, extracted from the Catalog of Isolated Galaxies and reevaluated morphologically in the context of the AMIGA project (Analysis of the interstellar Medium of Isolated GAlaxies). We focus on Sb-Sc morphological types, as they are the most representative population among the isolated spiral galaxies. Our analysis yields a large number of important galactic parameters and various correlation plots are used to seek relationships that might shed light on the processes involved in determining those parameters. Assuming that the bulge Sérsic index and/or Bulge/Total luminosity ratios are reasonable diagnostics for pseudo-versus classical bulges, we conclude that the majority of late-type isolated disk galaxies likely host pseudobulges rather than classical bulges. Our parametrization of galactic bulges and disks suggests that the properties of the pseudobulges are strongly connected to those of the disks. This may indicate that pseudobulges are formed through internal processes within the disks (i.e. secular evolution) and that bars may play an important role in their formation. Although the sample under investigation covers a narrow morphological range, a clear separation between Sb and Sbc-Sc types is observed in various measures, e.g. the former are redder, brighter, have larger disks and larger bars, more luminous bulges, are more concentrated, more symmetric and clumpier than the latter. A comparison with samples of spiral galaxies (within the same morphological range) selected without isolation criteria reveals that the isolated galaxies tend to host larger bars, are more symmetric, less concentrated and less clumpy.

Monthly Notices of the Royal Astronomical Society, 2015

We combine Herschel/SPIRE submillimetre (submm) observations with existing multiwavelength data to investigate the characteristics of low-redshift, optically red galaxies detected in submm bands. We select a sample of galaxies in the redshift range 0.01 ≤ z ≤ 0.2, having >5σ detections in the SPIRE 250 μm submm waveband. Sources are then divided into two sub-samples of red and blue galaxies, based on their UV-optical colours. Galaxies in the red sample account for ≈4.2 per cent of the total number of sources with stellar masses M * 10 10 M. Following visual classification of the red galaxies, we find that 30 per cent of them are early-type galaxies and 40 per cent are spirals. The colour of the red-spiral galaxies could be the result of their highly inclined orientation and/or a strong contribution of the old stellar population. It is found that irrespective of their morphological types, red and blue sources occupy environments with more or less similar densities (i.e. the 5 parameter). From the analysis of the spectral energy distributions of galaxies in our samples based on MAGPHYS, we find that galaxies in the red sample (of any morphological type) have dust masses similar to those in the blue sample (i.e. normal spiral/star-forming systems). However, in comparison to the red-spirals and in particular blue systems, red-ellipticals have lower mean dust-to-stellar mass ratios. Besides galaxies in the red-elliptical sample have much lower mean star formation/specific star formation rates in contrast to their counterparts in the blue sample. Our results support a scenario where dust in early-type systems is likely to be of an external origin.

2005

The method of the brightest star color distributions on the color-magnitude diagram is applied order to determine the foreground extinction toward two Im galaxies, seen through the Milky Way disk. The accuracy of the derived extinction values is estimated to be about 0.2 mag. The CCD photometry in V and I bands published by Karachentsev et al. (1997) is used. The extinction estimates toward UGCA 105 and UGCA 86 are 0.94 mag and 5.33 mag, respectively. They are significantly different from the catalogue values, 1.35 mag and 4.06.mag (Schlegel et al. 1998), but the most appropriate respective isochrones explain better the apparent color-magnitude diagrams. It seems that the brightest disk region of UGCA 86, known as VII Zw 9, is located along a sightline of lowered extinction

The Astronomical Journal, 1995

We present U BV I and Hα images of a sample of Low Surface Brightness (LSB) disk galaxies. These galaxies are generally late types, if they can be sensibly classified at all. However, they are not dwarfs, being intrinsically large and luminous.