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Late-type Galaxies (late-type + galaxy)

Distribution by Scientific Domains

Physics and Astronomy	100%

Selected Abstracts

The variation of the galaxy luminosity function with group properties

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2010
Aaron Robotham
ABSTRACT We explore the shape of the galaxy luminosity function (LF) in groups of different mass by creating composite LFs over large numbers of groups. Following previous work using total group luminosity as the mass indicator, here we split our groups by multiplicity and by estimated virial (group halo) mass, and consider red (passive) and blue (star-forming) galaxies separately. In addition, we utilize two different group catalogues (2PIGG and Yang et al.) in order to ascertain the impact of the specific grouping algorithm and further investigate the environmental effects via variations in the LF with position in groups. Our main results are that LFs show a steepening faint end for early-type galaxies as a function of group mass/multiplicity, with a much suppressed trend (evident only in high mass groups) for late-type galaxies. Variations between LFs as a function of group mass are robust irrespective of which grouping catalogue is used, and broadly speaking what method for determining group ,mass' is used. We find in particular that there is a significant deficit of low-mass passive galaxies in low-multiplicity groups, as seen in high-redshift clusters. Further to this, the variation in the LF appears to only occur in the central regions of systems, and in fact seems to be most strongly dependent on the position in the group relative to the virial radius. Finally, distance,rank magnitude relations were considered. Only the Yang groups demonstrated any evidence of a correlation between a galaxy's position relative to the brightest group member and its luminosity. 2PIGG possessed no such gradient, the conclusion being the friend-of-friend algorithm suppresses the signal for weak luminosity,position trends and the Yang grouping algorithm naturally enhances it. [source]

The nature of the Sloan Digital Sky Survey galaxies in various classes based on morphology, colour and spectral features , III.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2010
Environments
ABSTRACT We present a study on the environments of the Sloan Digital Sky Survey (SDSS) galaxies divided into fine classes based on their morphology, colour and spectral features. The SDSS galaxies are classified into early-type and late-type; red and blue; passive, H ii, Seyfert and low-ionization nuclear emission-line region (LINER), which returns a total of 16 fine classes of galaxies. We estimate the local number density, target-excluded local luminosity density, local colour, close pair fraction and the luminosity and colour of the brightest neighbour, which are compared between the fine classes comprehensively. The morphology,colour class of galaxies strongly depends on the local density, with the approximate order of high-density preference: red early-type galaxies (REGs); red late-type galaxies (RLGs); blue early-type galaxies (BEGs) and blue late-type galaxies (BLGs). We find that high-density environments (like cluster environments) seem to suppress active galactic nucleus activity. The pair fraction of H ii REGs does not show a statistically significant difference from that of passive REGs, while the pair fraction of H ii BLGs is smaller than that of non-H ii BLGs. H ii BLGs show obvious double (red + blue) peaks in the distribution of the brightest neighbour colour, while red galaxies show a single red peak. The brightest neighbours of Seyfert BLGs tend to be blue, while those of LINER BLGs tend to be red, which implies that the difference between Seyfert and LINER may be related to the pair interaction. Other various environments of the fine classes are investigated, and their implications for galaxy evolution are discussed. [source]

The velocity function of gas-rich galaxies

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2010
M. A. Zwaan
ABSTRACT We measure the distribution function of rotational velocities ,(Vc) of late-type galaxies from the HIPASS galaxy catalogue. Previous measurements of the late-type velocity function are indirect, derived by converting the galaxy luminosity function using the relation between galaxy luminosity and rotation velocity (the Tully,Fisher relation). The advantage of H i Parkes All Sky Survey is that space densities and velocity widths are both derived from the same survey data. We find good agreement with earlier inferred measurements of ,(Vc), but we are able to define the space density of objects with Vc as low as 30 km s,1. The measured velocity function is ,flat' (power-law slope ,,,1.0) below Vc, 100 km s,1. We compare our results with predictions based on , cold dark matter simulations and find good agreement for rotational velocities in excess of 100 km s,1, but at lower velocities current models over-predict the space density of objects. At Vc= 30 km s,1, this discrepancy is approximately a factor of 20. [source]

Variations in 24-,m morphologies among galaxies in the Spitzer Infrared Nearby Galaxies Survey: new insights into the Hubble sequence

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007
G. J. Bendo
ABSTRACT To study the distribution of star formation and dust emission within nearby galaxies, we measured five morphological parameters in the 3.6- and 24-,m wavebands for 65 galaxies in the Spitzer Infrared Nearby Galaxies Survey (SINGS) and eight galaxies that were serendipitously observed by SINGS. The morphological parameters demonstrate strong variations along the Hubble sequence, including statistically significant differences between S0/a-Sab and Sc-Sd galaxies. Early-type galaxies are generally found to be compact, centralized, symmetric sources in the 24-,m band, while late-type galaxies are generally found to be extended, asymmetric sources. These results suggest that the processes that increase the real or apparent sizes of galaxies' bulges also lead to more centralized 24-,m dust emission. Several phenomena, such as strong nuclear star formation, Seyfert activity, or outer ring structures, may cause galaxies to deviate from the general morphological trends observed at 24 ,m. We also note that the 24-,m morphologies of Sdm-Im galaxies are quite varied, with some objects appearing very compact and symmetric but others appearing diffuse and asymmetric. These variations reflect the wide variation in star formation in irregular galaxies as observed at other wavelengths. The variations in the 24-,m morphological parameters across the Hubble sequence mirror many of the morphological trends seen in other tracers of the ISM and in stellar emission. However, the 24-,m morphological parameters for the galaxies in this sample do not match the morphological parameters measured in the stellar wavebands. This implies that the distribution of dust emission is related to but not equivalent to the distribution of stellar emission. [source]

Halo model at its best: constraints on conditional luminosity functions from measured galaxy statistics

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2006
Asantha Cooray
ABSTRACT Using the conditional luminosity function (CLF; the luminosity distribution of galaxies in a dark matter halo) as the fundamental building block, we present an empirical model for the galaxy distribution. The model predictions are compared with the published luminosity function (LF) and clustering statistics from the Sloan Digital Sky Survey (SDSS) at low redshifts, galaxy correlation functions from the Classifying Objects by Medium-Band Observations 17 (COMBO-17) survey at a redshift of 0.6, the Deep Extragalactic Evolutionary Probe 2 (DEEP2) survey at a redshift of unity, the Great Observatories Deep Origins Survey (GOODS) at a redshift around 3 and the Subaru/XMM,Newton Deep Field data at a redshift of 4. The comparison with statistical measurements allows us to constrain certain parameters related to analytical descriptions on the relation between a dark matter halo and its central galaxy luminosity, its satellite galaxy luminosity, and the fraction of early- and late-type galaxies of that halo. With the SDSS r -band LF at Mr < ,17, the lognormal scatter in the central galaxy luminosity at a given halo mass in the central galaxy,halo mass, Lc(M), relation is constrained to be 0.17+0.02,0.01, with 1, errors here and below. For the same galaxy sample, we find no evidence for a low-mass cut-off in the appearance of a single central galaxy in dark matter haloes, with the 68 per cent confidence level upper limit on the minimum mass of dark matter haloes to host a central galaxy, with luminosity Mr < ,17, is 2 × 1010 h,1 M,. If the total luminosity of a dark matter halo varies with halo mass as Lc(M) (M/Msat),s when M > Msat, using SDSS data, we find that Msat= (1.2+2.9,1.1) × 1013 h,1 M, and power-law slope ,s= 0.56+0.19,0.17 for galaxies with Mr < ,17 at z < 0.1. At z, 0.6, the COMBO-17 data allows these parameters for MB < ,18 galaxies to be constrained as (3.3+4.9,3.0) × 1013 h,1 M, and (0.62+0.33,0.27), respectively. At z, 4, Subaru measurements constrain these parameters for MB < ,18.5 galaxies as (4.12+5.90,4.08) × 1012 h,1 M, and (0.55+0.32,0.35), respectively. The redshift evolution associated with these parameters can be described as a combination of the evolution associated with the halo mass function and the luminosity,halo mass relation. The single parameter well constrained by clustering measurements is the average of the total satellite galaxy luminosity corresponding to the dark matter halo distribution probed by the galaxy sample. For SDSS, ,Lsat,= (2.1+0.8,0.4) × 1010 h,2 L,, while for GOODS at z, 3, ,Lsat, < 2 × 1011 h,2 L,. For SDSS, the fraction of galaxies that appear as satellites is 0.13+0.03,0.03, 0.11+0.05,0.02, 0.11+0.12,0.03 and 0.12+0.33,0.05 for galaxies with luminosities in the r, band from ,22 to ,21, ,21 to ,20, ,20 to ,19 and ,19 to ,18, respectively. In addition to constraints on central and satellite CLFs, we also determine model parameters of the analytical relations that describe the fraction of early- and late-type galaxies in dark matter haloes. We use our CLFs to establish the probability distribution of halo mass in which galaxies of a given luminosity could be found either at halo centres or as satellites. Finally, to help establish further properties of the galaxy distribution, we propose the measurement of cross-clustering between galaxies divided into two distinctly different luminosity bins. Our analysis shows how CLFs provide a stronger foundation to built-up analytical models of the galaxy distribution when compared with models based on the halo occupation number alone. [source]

Extracting star formation histories from medium-resolution galaxy spectra

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2006
H. Mathis
ABSTRACT We adapt an existing data compression algorithm, moped, to the extraction of median-likelihood star formation histories from medium-resolution galaxy spectra. By focusing on the high-pass components of galaxy spectra, we minimize potential uncertainties arising from the spectrophotometric calibration and intrinsic attenuation by dust. We validate our approach using model high-pass spectra of galaxies with different star formation histories covering the wavelength range 3650,8500 Å at a resolving power of ,2000. We show that the method can recover the full star formation histories of these models, without prior knowledge of the metallicity, to within an accuracy that depends sensitively on the signal-to-noise ratio. The investigation of the sensitivity of the flux at each wavelength to the mass fraction of stars of different ages allows us to identify new age-sensitive features in galaxy spectra. We also highlight a fundamental limitation in the recovery of the star formation histories of galaxies for which the optical signatures of intermediate-age stars are masked by those of younger and older stars. As an example of application, we use this method to derive average star formation histories from the highest-quality spectra of typical (in terms of their stellar mass), morphologically identified early- and late-type galaxies in the Early Data Release (EDR) of the Sloan Digital Sky Survey (SDSS). We find that, in agreement with the common expectation, early-type galaxies must have formed most of their stars over 8 Gyr ago, although a small fraction of the total stellar mass of these galaxies may be accounted for by stars with ages down to 4 Gyr. In contrast, late-type galaxies appear to have formed stars at a roughly constant rate. We also investigate the constraints set by the high-pass signal in the stacked spectra of a magnitude-limited sample of 20 623 SDSS-EDR galaxies on the global star formation history of the Universe and its distribution among galaxies in different mass ranges. We confirm that the stellar populations in the most massive galaxies today appear to have formed on average earlier than those in the least massive galaxies. Our results do not support the recent suggestion of a statistically significant peak in the star formation activity of the Universe at redshifts below unity, although such a peak is not ruled out. [source]

Star formation in close pairs selected from the Sloan Digital Sky Survey

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2004
B. Nikolic
ABSTRACT The effect of galaxy interactions on star formation has been investigated using Data Release One of the Sloan Digital Sky Survey (SDSS). Both the imaging and spectroscopy data products have been used to construct a catalogue of nearest companions to a volume-limited (0.03 < z < 0.1) sample of galaxies drawn from the main galaxy sample of SDSS. Of the 13 973 galaxies in the volume-limited sample, we have identified 12 492 systems with companions at projected separations less than 300 kpc. Star formation rates for the volume-limited sample have been calculated from extinction and aperture corrected H, luminosities and, where available, IRAS data. Specific star formation rates were calculated by estimating galaxy masses from z -band luminosities, and r -band concentration indices were used as an indicator of morphological class. The mean specific star formation rate is significantly enhanced for projected separations less than 30 kpc. For late-type galaxies, the correlation extends out to projected separations of 300 kpc and is most pronounced in actively star-forming systems. The specific star formation rate is observed to decrease with increasing recessional velocity difference, but the magnitude of this effect is small compared to that associated with the projected separation. We also observe a tight relationship between the concentration index and pair separation; the mean concentration index is largest for pairs with separations of approximately 75 kpc and declines rapidly for separations smaller than this. This is interpreted as being due to the presence of tidally triggered nuclear starbursts in close pairs. Further, we find no dependence of star formation enhancement on the morphological type or mass of the companion galaxy. [source]

Quantitative morphological analysis of the Hubble Deep Field North and Hubble Deep Field South , I. Early- and late-type luminosity,size relations of galaxies out to z, 1

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2004
I. Trujillo
ABSTRACT Based on drizzled F606W and F814W images, we present quantitative structural parameters in the V -band rest-frame for all galaxies with z < 1 and I814(AB) < 24.5 mag in the Hubble Deep Fields North and South. Our structural parameters are based on a two-component surface brightness distribution using a Sérsic bulge and an exponential disc. Detailed simulations and comparisons with previous work are presented. The luminosity,size distribution of early-type galaxies is consistent with the hypothesis that their structural properties were already in place by z, 1 and have evolved passively since then; early-type galaxies were ,1.35(±0.1) mag brighter in rest-frame V -band luminosity at z, 0.7 than now. Compared with present-day late-type galaxies, those at z, 0.7 with LV > 0.2 × 1010 h,2 L, show a moderate decrease [,30(±10) per cent] in size [or interpreted differently, a decrease of ,0.77(±0.30) mag in the central surface brightness] at a given luminosity. Finally, we make a comparison of our results with the infall and hierarchical models. [source]

Dust emission in the far-infrared as a star formation tracer at z= 0: systematic trends with luminosity

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2003
D. Pierini
ABSTRACT We investigate whether dust emission in the far-infrared (far-IR) continuum provides a robust estimate of the star formation rate (SFR) for a nearby, normal late-type galaxy. We focus on the ratio of the 40,1000 ,m luminosity (Ldust) to the far-ultraviolet (far-UV) (0.165 ,m) luminosity, which is connected to recent episodes of star formation. Available total photometry at 0.165, 60, 100 and 170 ,m limits the statistics to 30 galaxies, which, however, span a large range in observed (and, thus, attenuated by dust) K -band (2.2 ,m) luminosity, morphology and inclination (i). This sample shows that the ratio of Ldust to the observed far-UV luminosity depends not only on i, as expected, but also on morphology and, in a tighter way, on observed K -band luminosity. We find that Ldust/LFUV, eLK0.62, where LFUV and LK are the unattenuated stellar luminosities in far-UV and K, respectively, and , is the ratio of the attenuation optical depths at 0.165 ,m (,FUV) and 2.2 ,m (,K). This relation is to zeroth order independent of i and morphology. It may be further expressed as Ldust/LFUV,L,K, where ,= 0.61 , 0.02,, under the observationally motivated assumption that, for an average inclination, e,L,0.02K. We adopt calculations of two different models of attenuation of stellar light by internal dust to derive solid-angle-averaged values of ,. We find that , is positive and decreases towards 0 from the more luminous to the less luminous galaxies. This means that there is no universal ratio of far-IR luminosity to unattenuated far-UV luminosity for nearby, normal late-type galaxies. The far-IR luminosity systematically overestimates SFR in more luminous, earlier-type spirals, owing to the increased fractional contribution to dust heating of optical/near-IR photons in these objects. Conversely, it systematically underestimates SFR in fainter, later-type galaxies, the ,FUV of which is reduced. The limited statistics and the uncertainty affecting the previous scaling relations do not allow us to establish quantitative conclusions, but an analogous analysis making use of larger data sets, available in the near future (e.g. from GALEX, ASTRO-F and SIRTF), and of more advanced models will allow a quantitative test of our conclusions. [source]

The redshift distribution of FIRST radio sources at 1 mJy

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2000
M. Magliocchetti
We present spectra for a sample of radio sources from the FIRST survey, and use them to define the form of the redshift distribution of radio sources at mJy levels. We targeted 365 sources and obtained 46 redshifts (13 per cent of the sample). We find that our sample is complete in redshift measurement to R,18.6, corresponding to z,0.2. Galaxies were assigned spectral types based on emission-line strengths. Early-type galaxies represent the largest subset (45 per cent) of the sample and have redshifts 0.15,z,0.5; late-type galaxies make up 15 per cent of the sample and have redshifts 0.05,z,0.2; starbursting galaxies are a small fraction (,6 per cent), and are very nearby (z,0.05). Some 9 per cent of the population have Seyfert 1/quasar-type spectra, all at z,0.8, and 4 per cent are Seyfert 2 type galaxies at intermediate redshifts (z,0.2). Using our measurements and data from the Phoenix survey (Hopkins et al.), we obtain an estimate for N(z) at S1.4 GHz,1 mJy and compare this with model predictions. At variance with previous conclusions, we find that the population of starbursting objects makes up ,5 per cent of the radio population at S,1 mJy. [source]

Probing evolutionary mechanisms in galaxy clusters: H I in Abell 1367

ASTRONOMISCHE NACHRICHTEN, Issue 9-10 2009
T.C. Scott
Abstract We are carrying out a programme of CO and interferometric H I observations in the nearby galaxy cluster Abell 1367. The aim is to better understand the processes driving the evolution of the ISM in late-type galaxies in the cluster environment. Abell 1367 is a dynamically young cluster. We have determined the H I content and g , i colour from AGES (Cortese 2008) and SDSS, respectively, of its bright late-type galaxies (spirals) in a volume centred on the NW subcluster. We use a combination of these characteristics, both of which are indicative of evolutionary history, to classify each spiral into one of four evolutionary states. This analysis revealed the cluster contains spirals in a wide range of evolutionary states. VLA D-array imaging centred on the NW subcluster indicates most galaxies in that field have their H I intensity maximum offset relative to its optical counterpart, implying a recent and strong disturbance. The direction of this offset is not always consistent with a simple scenario of ram pressure stripping by the cluster's high density intra-cluster medium (ICM) (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Testing of the dwarf galaxy content and the evolutionary status of nearby groups of galaxies

ASTRONOMISCHE NACHRICHTEN, Issue 9-10 2009
J. Vennik
Abstract We carried out visual and parametric searches for dwarf galaxies in five loose groups of galaxies. Follow-up spectroscopy with the HET has shown a 50% success rate of morphological selection. The evolutionary status of the studied groups differs: while the NGC 6962 group has a partially relaxed core, surrounded by an infall region, the NGC 5005/5033 group and the IC 65 group, which consist only of late-type galaxies, are probably still assembling (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Morphological properties of isolated galaxies vs. isolation criteria

ASTRONOMISCHE NACHRICHTEN, Issue 9-10 2009
I.B. Vavilova
Abstract We studied the morphological properties of isolated galaxies samples in dependence on the isolation parameter and properties of primary catalogs. With this aim we identified the samples of single and isolated galaxies from SDSS DR5 (Single and QIsol) with the 3D Voronoi tessellation method (Elyiv et al. 2009). We found that in comparison with other samples of isolated galaxies, the QIsol sample contains an excess of late-type galaxies, especially with a low luminosity and BCG/Im/Irr morphology. We also showed that the fractions of early type galaxies in QIsol SDSS DR5 sample and samples 2MIG (Karachentseva et al. 2010) and CIG (Karachentseva et al. 1973; Hernandez-Toledo et al. 2008) are in a good agreement (16,19 %), but Allam's (Allam et al. 2005) and Prada's (Prada et al. 2003) SDSS DR1 samples show a higher excess of the early type galaxies that can be explained by the selection criteria and morphology definition method. We found a weak relation between isolation parameter and color index for the Single sample that may indicate that even in the low dense environment the morphology density relation is observed. We conclude that morphological properties of the resulting sample of isolated galaxies are highly dependent on the primary catalogue from which the galaxies were selected. Moreover, the selection criterion is also important but plays a secondary role in the resulting morphological content, color indices distribution and other parameters of the isolated galaxy samples. Only four galaxies are common in the 2MIG, QIsol, and CIG samples, namely UGC5184, UGC6121, UGC8495, and UGC9598, that allows to consider them as really most isolated galaxies (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]