Early-type Sample Research Articles

Galaxy mass-size segregation in the cosmic web from the CAVITY parent sample

The mass-size relation is a fundamental galaxy scaling relation that is intrinsically linked to galaxy formation and evolution. The physical processes involved in galaxy growth leave their particular imprint on the relation between the stellar or total mass and galaxy size. We aim to explore the effect of the large-scale environment on the stellar mass-size relation using samples and a selection of added-value products from the Calar Alto Void Integral-field Treasury surveY (CAVITY) collaboration. We analysed the Petrosian R50 and R90 radii from SDSS DR16 images of a sample of ≈ 14000 galaxies inhabiting cosmic voids, filaments and walls, and clusters, with a stellar mass range between rm 10^ M_⊙. We investigated the mass-size relation with respect to the galaxy morphology, as well as with the star formation history (SFH), parametrised across a range of different timescales (rm T_ rm T_ and rm T_ We find that, on average, early-type galaxies in voids are approximately 10-20% smaller than their counterparts in denser environments, such as filaments, walls, and clusters, regardless of when they assembled their mass. Additionally, evidence suggests that the mass-size relation for the more massive void galaxies within the early-type sample exhibits a shallower slope, compared to galaxies in denser large-scale environments. In contrast, early-type galaxies in filaments, walls, and clusters exhibit a more consistent mass-size distribution. For stellar masses of rm log(M_⋆ / M_⊙ ) = 9 - 10.5, late-type cluster galaxies are smaller and more concentrated than those in lower density environments, such as filaments, walls, and voids; whereas void and filament+wall galaxies exhibit similar size and concentration values. However, for galaxies with masses above rm 10^ M_⊙, the sizes of void galaxies become comparable to those in clusters. The trend of smaller low-mass cluster galaxies is primarily driven by galaxies with rm T_ greater than 7 Gyr. We conclude that the large-scale environment influences the mass-size relation of galaxies. Assuming that early-type galaxies undergo two growth phases, we find that they primarily grow their mass during the first phase of formation. In voids, the subsequent size growth from minor mergers is less pronounced. This is likely due to slower evolution and reduced minor merger activity or the fact that the void environment inherently has fewer accretion events, or even a combination of these effects. The change in slope for high-mass void galaxies suggests a lower rate of minor accretion. This trend is also evident in late-type void galaxies with masses above rm ≈ 10^ M_⊙, where minor mergers contribute to their size growth. In contrast, late-type quenched cluster galaxies are smaller in size due to interactions within the cluster environment, with early infallers being more strongly affected by these environmental interactions.

Radio continuum from the most massive early-type galaxies detected with ASKAP RACS

Abstract All very massive early-type galaxies contain supermassive blackholes, but are these blackholes all sufficiently active to produce detectable radio continuum sources? We have used the 887.5 MHz Rapid ASKAP Continuum Survey DR1 to measure the radio emission from morphological early-type galaxies brighter than $K_S=9.5$ selected from the 2MASS Redshift Survey, HyperLEDA, and RC3. In line with previous studies, we find median radio power increases with infrared luminosity, with $P_{1.4} \propto L_K^{2.2}$ , although the scatter about this relation spans several orders of magnitude. All 40 of the $M_K<-25.7$ early-type galaxies in our sample have measured radio flux densities that are more than $2\sigma$ above the background noise, with $1.4\,{\rm GHz}$ radio powers spanning ${\sim} 3 \times 10^{20}$ to ${\sim} 3\times 10^{25}\,{\rm W/Hz^{-1}}$ . Cross-matching our sample with integral field spectroscopy of early-type galaxies reveals that the most powerful radio sources preferentially reside in galaxies with relatively low angular momentum (i.e. slow rotators). While the infrared colours of most galaxies in our early-type sample are consistent with passive galaxies with negligible star formation and the radio emission produced by active galactic nuclei or AGN remnants, very low levels of star formation could power the weakest radio sources with little effect on many other star formation rate tracers.

Exploring the Stellar Rotation of Early-type Stars in the LAMOST Medium-resolution Survey. I. Catalog

Abstract We derive stellar parameters and abundances (“stellar labels”) of 40,034 late-B and A-type main-sequence stars extracted from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope Medium Resolution Survey (LAMOST–MRS). The primary selection of our early-type sample was obtained from LAMOST Data Release 7 based on spectral-line indices. We employed the Stellar Label Machine to derive their spectroscopic stellar parameters, drawing on Kurucz spectral synthesis models with 6000 < T eff < 15,000 K and −1 < [M/H] < 1 dex. For a signal-to-noise ratio of ∼60, the cross validated scatter is ∼75 K, 0.06 dex, 0.05 dex, and ∼3.5 km s−1 for T eff, log g , [M/H], and v sin i , respectively. A comparison with objects with prior known stellar labels shows great consistency for all stellar parameters, except for log g . Although this is an intrinsic caveat that comes from the MRS’s narrow wavelength coverage, it only has a minor effect on estimates of the stellar rotation rates because of the decent spectral resolution and the profile-fitting method employed. The masses and ages of our early-type sample stars were inferred from nonrotating stellar evolution models. This paves the way for reviewing the properties of stellar rotation distributions as a function of stellar mass and age.

MegaMorph: classifying galaxy morphology using multi-wavelength Sérsic profile fits

Aims. This work investigates the potential of using the wavelength-dependence of galaxy structural parameters (S\'ersic index, n, and effective radius, Re) to separate galaxies into distinct types. Methods. A sample of nearby galaxies with reliable visual morphologies is considered, for which we measure structural parameters by fitting multi-wavelength single-S\'ersic models. Additionally, we use a set of artificially redshifted galaxies to test how these classifiers behave when the signal-to-noise decreases. Results. We show that the wavelength-dependence of n may be employed to separate visually-classified early- and late-type galaxies, in a manner similar to the use of colour and n. Furthermore, we find that the wavelength variation of n can recover galaxies that are misclassified by these other morphological proxies. Roughly half of the spiral galaxies that contaminate an early-type sample selected using (u-r) versus n can be correctly identified as late-types by N, the ratio of n measured in two different bands. Using a set of artificially-redshifted images, we show that this technique remains effective up to z ~ 0.1. N can therefore be used to achieve purer samples of early-types and more complete samples of late-types than using a colour-n cut alone. We also study the suitability of R, the ratio of Re in two different bands, as a morphological classifier, but find that the average sizes of both early- and late-type galaxies do not change substantially over optical wavelengths.

A tool for the morphological classification of galaxies: the concentration index

Using galaxy data from the Sloan Digital Sky Survey Data Release 8, I explore whether the concentration index is a good morphological classification tool and find that a reasonable sample of pure late-type galaxies can be constructed with the choice of the r-band concentration index ci=2.85. The opposite is not true, however, due to the fairly high contamination of an early-type sample by late-type galaxies. In such an analysis, the influence of selection effects is less important. To disentangle correlations of the morphology and concentration index with stellar mass, star formation rate (SFR), specific star formation rate (SSFR) and active galactic nucleus (AGN) activity, I investigate correlations of the concentration index with these properties at a fixed morphology and correlations of the morphology with these properties at a fixed concentration index. It is found that at a fixed morphology, high-concentration galaxies are preferentially more massive and have a lower SFR and SSFR than low-concentration galaxies, whereas at a fixed concentration index, elliptical galaxies are preferentially more massive and have a lower SFR and SSFR than spiral galaxies. This result shows that the stellar mass, SFR and SSFR of a galaxy are correlated with its concentration index as well as its morphology. In addition, I note that AGNs are preferentially found in more concentrated galaxies only in the sample of spiral galaxies.

A HIGH-RESOLUTION STUDY OF THE ATOMIC HYDROGEN IN CO-RICH EARLY-TYPE GALAXIES

We present an analysis of new and archival Very Large Array H i observations of a sample of 11 early-type galaxies rich in CO, with detailed comparisons of CO and H i distributions and kinematics. The early-type sample consists of both lenticular and elliptical galaxies in a variety of environments. A range of morphologies and environments were selected in order to give a broader understanding of the origins, distribution, and fate of the cold gas in early-type galaxies. Six of the eleven galaxies in the sample are detected in both H i and CO. The H2 to H i mass ratios for this sample range from 0.2 to 120. The H i morphologies of the sample are consistent with that of recent H i surveys of early-type galaxies, which also find a mix of H i morphologies and masses, low H i peak surface densities, and a lack of H i in early-type galaxies that reside in high-density environments. The HI-detected galaxies have a wide range of H i masses (1.4 × 106 to 1.1 × 1010 M☉). There does not appear to be any correlation between the H i mass and morphology (E versus S0). When H i is detected, it is centrally peaked—there are no central kiloparsec-scale central H i depressions like those observed for early-type spiral galaxies at similar spatial resolutions and scales. A kinematic comparison between the H i and CO indicates that both cold gas components share the same origin. The primary goal of this and a series of future papers is to better understand the relationship between the atomic and molecular gas in early-type galaxies, and to compare the observed relationships with those of spiral galaxies where this relationship has been studied in depth.

CONSTRAINTS ON FEEDBACK PROCESSES DURING THE FORMATION OF EARLY-TYPE GALAXIES

Galaxies are found to obey scaling relations between a number of observables. These relations follow different trends at the low- and the high-mass ends. The processes driving the curvature of scaling relations remain uncertain. In this letter, we focus on the specific family of early-type galaxies, deriving the star formation histories of a complete sample of visually classified galaxies from SDSS-DR7 over the redshift range 0.01<z<0.025, covering a stellar mass interval from 10^9 to 3 x 10^11 Msun. Our sample features the characteristic "knee" in the surface brightness vs. mass distribution at Mstar~3 x 10^10 Msun. We find a clear difference between the age and metallicity distributions of the stellar populations above and beyond this knee, which suggests a sudden transition from a constant, highly efficient mode of star formation in high-mass galaxies, gradually decreasing towards the low-mass end of the sample. At fixed mass, our early-type sample is more efficient in building up the stellar content at early times in comparison to the general population of galaxies, with half of the stars already in place by redshift z~2 for all masses. The metallicity-age trend in low-mass galaxies is not compatible with infall of metal-poor gas, suggesting instead an outflow-driven relation.

Reconstructing galaxy fundamental distributions and scaling relations from photometric redshift surveys. Applications to the SDSS early-type sample

Noisy distance estimates associated with photometric rather than spectroscopic redshifts lead to a mis-estimate of the luminosities, and produce a correlated mis-estimate of the sizes. We consider a sample of early-type galaxies from the SDSS DR6 for which both spectroscopic and photometric information is available, and apply the generalization of the V_max method to correct for these biases. We show that our technique recovers the true redshift, magnitude and size distributions, as well as the true size-luminosity relation. We find that using only 10% of the spectroscopic information randomly spaced in our catalog is sufficient for the reconstructions to be accurate within about 3%, when the photometric redshift error is dz = 0.038. We then address the problem of extending our method to deep redshift catalogs, where only photometric information is available. In addition to the specific applications outlined here, our technique impacts a broader range of studies, when at least one distance-dependent quantity is involved. It is particularly relevant for the next generation of surveys, some of which will only have photometric information.

THE DEPENDENCE OF LUMINOSITY AND g – r COLOR ON THE ENVIRONMENT FOR THE SAME MORPHOLOGICAL TYPES

We divide the volume-limited main galaxy sample of the Sloan Digital Sky Survey Data Release 6 (SDSS DR6) into two samples—the early-type sample and the late-type sample—to investigate the dependence of luminosity and g – r color on the environment for the same morphological types. For each sample, we construct two subsamples at both extremes of local density which is measured within the distance to the fifth nearest neighbor. It turns out that, for the early-type sample and the late-type sample, significant correlation between g – r color and the environment still exists, but the correlation in the late-type sample is much stronger than that in the early-type sample. Our studies also suggest that the dependence of luminosity on the local environment is mainly due to the dependence of galaxy morphologies on the local environment and the correlation between morphologies and luminosity.

Clustering properties of galaxies with different galaxy morphologies

From the volume-limited main galaxy sample of the Sloan Digital Sky Survey Data Release 6 (SDSS DR6), we construct an early-type sample and a late-type sample, and perform comparative studies of clustering properties between them. It is found that the distribution of late-type galaxies is more filamentary. In addition, in the late-type sample, the fractions of single, close double and multiple galaxies are higher than the ones of the early-type sample, but the fraction of grouped galaxies is lower. We also randomly extract a subsample from the late-type sample, which has the same galaxy number and number density as the early-type sample, compare clustering properties of this subsample with ones of the early-type sample, and reach the same conclusions.

Current star formation in early-type galaxies and the KA phenomenon

We present the results of an effort to identify and study a sample of the likely progenitors of elliptical (E) and lenticular (S0) K+A galaxies. To achieve this, we have searched a sample ∼11 000 nearby (m r < 16) early-type galaxies selected by morphology from the Sloan Digital Sky Survey (SDSS) main spectroscopic sample for actively star-forming E and S0 galaxies. Using emission-line ratios and visual inspection of SDSS g-band images, we have identified 335 galaxies from the SDSS Fourth Data Release (DR4) as actively star-forming E and S0 galaxies. These galaxies make up about 3 per cent of the total early-type sample and less than 1 per cent of all main galaxies with m r < 16. We also identified a sample of ∼400 K+A galaxies from DR4 with m r < 16; more than half of these are E and S0 galaxies. We find that star-forming early-type galaxies and K+A galaxies have similar mass distributions; they are on average less massive than typical early-type galaxies but more massive than the average starforming galaxy. Both of these types of galaxies are found in higher fractions among all galaxies in lower density environments. The fractions of star-forming E and S0 galaxies and E and S0 K+A galaxies depend on environment in nearly the same way. Model spectra fit to the stellar continua of the star-forming E and S0 galaxies showed that their properties are consistent with star formation episodes of � 1 Gyr in duration. The modelling results imply that on average, the star formation episodes will increase the stellar masses by about 4 per cent. The results also imply that only episodes that increase the stellar mass by more than 2‐5 per cent will lead to K+A galaxies as we have defined them and that this is true for roughly 80 per cent of the star-forming E and S0 galaxies in our sample. The estimated typical increase in stellar mass

The Globular Cluster Systems of the Early-Type Galaxies NGC 3379, NGC 4406, and NGC 4594 and Implications for Galaxy Formation

We have investigated the global properties of the globular cluster (GC) systems of three early-type galaxies: the Virgo Cluster elliptical NGC 4406, the field elliptical NGC 3379, and the field S0 galaxy NGC 4594. These galaxies were observed as part of a wide-field CCD survey of the GC populations of a large sample of normal galaxies beyond the Local Group. Images obtained with the Mosaic detector on the Kitt Peak 4 m telescope provide radial coverage to at least 24', or ~70–100 kpc. We use BVR photometry and image classification to select GC candidates and thereby reduce contamination from non-GCs, as well as Hubble Space Telescope WFPC2 data to help quantify the contamination that remains. The GC systems of all three galaxies have color distributions with at least two peaks and show modest negative color gradients. The proportions of blue GCs range from 60% to 70% of the total populations. The GC specific frequency (SN) of NGC 4406 is 3.5 ± 0.5, ~20% lower than past estimates and nearly identical to SN for the other Virgo Cluster elliptical included in our survey, NGC 4472. SN for NGC 3379 and NGC 4594 are 1.2 ± 0.3 and 2.1 ± 0.3, respectively; these are similar to past values, but the errors have been reduced by a factor of 2–3. We compare our results for the early-type sample (including NGC 4472) to models for the formation of massive galaxies and their GC systems. Of the scenarios we consider, a hierarchical merging picture, in which metal-poor GCs form at high redshift in protogalactic building blocks and metal-rich GC populations are built up over time during subsequent gas-rich mergers, appears most consistent with the data.

Application of the Limit-Cycle Model to Star Formation Histories in Spiral Galaxies: Variation among Morphological Types

We propose a limit-cycle scenario of star formation history for any morphological type of spiral galaxy. It is known observationally that an early-type spiral sample has a wider range of present star formation rate (SFR) than a late-type sample. This tendency is understood in the framework of the limit-cycle model of the interstellar medium (ISM), in which the SFR changes cyclically in accordance with the temporal variation of the mass fraction of the three ISM components. When the limit-cycle model of the ISM is applied, the amplitude of variation of the SFR is expected to change with the supernova (SN) rate. Observational evidence indicates that early-type spiral galaxies should show smaller rates of present SNe than late-type ones. Combining this evidence with the limit-cycle model of the ISM, we predict that the early-type spiral galaxies will show larger amplitudes in their SFR variation than the late types. Indeed, this prediction is consistent with the observed wider range of the SFR in the early-type sample than in the late-type sample. Thus, in the framework of the limit-cycle model of the ISM, we are able to interpret the difference in the amplitude of SFR variation among the morphological classes of spiral galaxies.

Tracing the vertical composition of disc galaxies through colour gradients

Optical observations of a statistically complete sample of edge-on disc-dominated galaxies are used to study the intrinsic vertical colour gradients in the galactic discs, in order to constrain the effects of population gradients, residual dust extinction and gradients in the metal abundance of the galaxies. For the majority of our sample galaxies, the colours and colour gradients in the range 1.0hz|z|3.0hz most likely reflect the intrinsic galactic properties (where hz is the vertical scaleheight). It appears that the intrinsic vertical colour gradients are either non-existent, or small and relatively constant as a function of position along the major axes of the galaxies. On average, the earlier-type galaxies exhibit smaller vertical (B−I) gradients than the later types; our results are consistent with the absence of any vertical colour gradient in the discs of the early-type sample galaxies. In most galaxies small-scale variations in the magnitude and even the direction of the vertical gradient are observed: at larger galactocentric distances they generally display redder colours with increasing z height, whereas the opposite is often observed in and near the galactic centres. For a significant fraction of our sample galaxies another mechanism in addition to the effects of stellar population gradients is required to explain the magnitude of the observed gradients. The non-zero colour gradients in a significant fraction of our sample galaxies are likely to be (at least) partially due to residual dust extinction at these z heights, as is also evidenced from the sometimes significant differences between the vertical colour gradients measured on either side of the galactic planes. We suggest that initial vertical metallicity gradients, if any, have probably not been accentuated by accretion or merging events over the lifetimes of our sample galaxies. On the other hand, they may have weakened any existing vertical metallicity gradients, although they also may have left the existing correlations unchanged.

Radio Structures of Seyfert Galaxies. VIII. A Distance‐ and Magnitude‐Limited Sample of Early‐Type Galaxies

The VLA has been used at 3.6 and 20 cm to image a sample of about 50 early-type Seyfert galaxies with recessional velocities less than 7000 km s-1 and total visual magnitude less than 14.5. Emission-line ([O III] and Hα+[N II]) and continuum (green and red) imaging of this sample has been presented in a previous paper. In this paper, we present the radio results, discuss statistical relationships between the radio and other properties, and investigate these relationships within the context of unified models of Seyferts. The mean radio luminosities of early-type Seyfert 1's (i.e., Seyfert 1.0's, 1.2's, and 1.5's) and 2.0's are found to be similar (consistent with the unified scheme), and the radio luminosity is independent of morphological type within this sample. The fraction of resolved radio sources is larger in the Seyfert 2.0's (93%) than in the Seyfert 1's (64%). However, the mean radio extents of Seyfert 2.0's and 1's are not significantly different, although this result is limited by the small number of resolved Seyfert 1's. The nuclear radio structures of Seyfert 2.0's in the early-type sample tend to be aligned with the [O III] and Hα+[N II] structures, even though the radio extents are smaller than the [O III] and Hα+[N II] extents by a factor of ~2 to more than 5. This alignment, previously known for individual Seyferts with linear radio sources, is here shown to be characteristic of early-type Seyfert galaxies as a class. Seyfert 2.0's in the early-type sample also show a significant alignment between the emission-line ([O III] and Hα+[N II]) axes and the major axis of the host galaxy. These alignments are consistent with a picture in which the ionized gas represents ambient gas predominantly coplanar with the galaxy stellar disk. This ambient gas is ionized by nuclear radiation that may escape preferentially along and around the radio axis, and is compressed in shocks driven by the radio ejecta. We use this alignment to constrain the product of the velocity of the radio ejecta and the period of any large-angle precession of the inner accretion disk and jet: Vejecta × P ≥ 2 kpc. An investigation of a larger sample of Seyferts reveals the unexpected result that the Seyfert 1's with the largest radio extent (≥1.5 kpc) are all of type Seyfert 1.2. It appears that classification as this type of intermediate Seyfert depends on some factor other than the relative orientation of the nuclear-obscuring torus to the line of sight. Among all the other Seyferts, the distribution of radio extent with Seyfert intermediate type is consistent with the expectations of the unified scheme.