Early-type Spiral Galaxies Research Articles

A Detailed Photometric Analysis of Early-Type Spiral Galaxies in Pairs

This project explores the relative role of “nature versus nurture” (intrinsically versus environmentally driven influences) in shaping the morphology and evolution of galaxies by performing a detailed photometric analysis of early-type spiral galaxies found in galaxy pairs. We use Fourier analysis to model the properties of the spiral arms and bulge/disk/bar decomposition analysis to find the properties of the bulge, disk, and bar of each spiral galaxy within our sample. We investigate the effect environmental density has on the formation and evolution of early-type galaxies by comparing our results with previous work done for samples of early-type galaxies found in different environments (isolated and loose groups). This analysis will allow us to gain more insight into the formation and evolution of spiral galaxies across a range of environments.

Morphological Decomposition of the Early-type Spiral Galaxy M81 (NGC 3031)

This paper presents a morphological investigation of the early-type spiral galaxy M81 (NGC 3031) through decomposition by fitting radial profiles of surface brightness using the software GALFIT, aimed at exploring structural components of M81 and quantifying their morphology. In this work, we adopt 6 types of decompositions with different numbers of morphological components, among which the most complicated one contains 5 components such as a bulge, a disk, a pair of outer spiral arms, a pair of inner spiral arms, and a galactic nucleus. The results show that, M81 hosts a classical bulge with the Sérsic index ∼ 5.0; the morphology and the luminosity for the bulge are almost constant in the different decomposition types. The disk of M81 has the Sérsic index ∼ 1.2 but the morphology and the luminosity are found sensitive to the inclusion of the inner spiral arms in the decomposition or not. The results of this work indicate that the combination of individual substructures has a considerable impact on the morphology of the galaxy as a mixture. On the basis of the results, the usability of the different types of decomposition is suggested in this work. The three-component decomposition, i.e., bulge + disk + nucleus, is applicable to statistics of large samples of galaxies; more complicated decomposition with spiral arms taken into account is suitable for precise measurements of individual galaxies in small samples. This work is based on the single-band Spitzer-The Infrared Array Camera (IRAC) 4.5 μm image. In the future, we will carry out multi-wavelength decomposition, for the purpose of investigating spectral energy distributions and stellar population properties for the galactic substructures, and thereby deduce their formation history and evolution processes.

Multiwavelength Bulge–Disk Decomposition for the Galaxy M81 (NGC 3031). I. Morphology

A panchromatic investigation of morphology for the early-type spiral galaxy M81 is presented in this paper. We perform bulge–disk decomposition in M81 images at a total of 20 wave bands from far-UV to near-IR (NIR) obtained with GALEX, Swift, Sloan Digital Sky Survey, WIYN, Two Micron All Sky Survey, Wide-field Infrared Survey Explorer, and Spitzer. Morphological parameters such as Sérsic index, effective radius, position angle, and axis ratio for the bulge and the disk are thus derived at all of the wave bands, which enables quantifying the morphological K-correction for M81 and makes it possible to reproduce images for the bulge and the disk in the galaxy at any wave band. The morphology as a function of wavelength appears as a variable-slope trend of the Sérsic index and the effective radius, in which the variations are steep at UV–optical and shallow at optical–NIR bands; the position angle and the axis ratio keep invariable at least at optical–NIR bands. It is worth noting that the Sérsic index for the bulge reaches ∼4–5 at optical and NIR bands, but drops to ∼1 at UV bands. This difference brings forward a caveat that a classical bulge is likely misidentified for a pseudobulge or no bulge at high redshifts where galaxies are observed through rest-frame UV channels with optical telescopes. The next work of this series is planned to study spatially resolved spectral energy distributions for the bulge and the disk, respectively, and thereby explore stellar population properties and star formation/quenching history for the galaxy composed of the subsystems.

Bulgeless disks, dark galaxies, inverted color gradients, and other expected phenomena at higher z

The spectral energy distribution (SED) of galaxies varies both between galaxies and within them. For instance, early-type spiral galaxies have a red bulge surrounded by a bluer star-forming disk with H II regions within. When observing redshifted galaxies, a given photometric filter probes light at a bluer rest frame, and in relating the observed magnitudes to the rest frame of the filter, so-called k corrections are commonly applied to account for the relative dimming or brightening in addition to the pure distance effect. The amount of correction depends on the shape of the spectrum (SED), so different k corrections apply to galaxies of different spectral types. This is, however, only part of the story, since any galaxy with a spatially non-homogeneous SED will experience a spatially varying relative dimming or brightening as a function of observed wavelength. Also, the morphological appearance of galaxies will therefore change with redshift. For instance, an early spiral galaxy observed in the V band would show a prominent bulge at z = 0, whereas, if at redshift z ∼ 1, the V filter probes emission in the rest-frame near-ultraviolet where the bulge is faint and the disk relatively brighter, thus the galaxy may appear as bulgeless. One popular way of studying spatial variations in the stellar population and dust content of galaxies is the use of color maps. For star-forming galaxies that have an appreciable contribution from nebular emission (lines and continuum), an additional effect is that the shifting of strong features in or out of filters will result in a non-monotonous color evolution with redshift. Hence, unlike the effects of distance, cosmological surface brightness dimming, and gravitational lensing, which are all achromatic, the fact that most galaxies have a spatially varying SED leads to a chromatic surface brightness modulation (CMOD) with redshift. While the CMOD effects are in principle easy to grasp, they affect multicolor imaging surveys and photometric properties derived from such surveys in a complex fashion. Properties such as the bulge-to-disk ratio, Sérsic exponent, light concentration, asymmetry index and effective radius, radial color gradients, and stellar mass determinations from SED fitting will depend on the redshift, the filters employed, and the rest-frame 2D SED patterns in a galaxy and will bias results inferred on galaxy evolution across cosmic time (e.g., the evolution of the mass-size, bulge-supermassive black hole, and Tully-Fisher relation), and potentially also weak lensing, if these effects are not properly taken into account. In this article we quantify the CMOD effects for idealized galaxies built from spectral synthesis models and from galaxies with observed integral field spectroscopy, and we show that they are significant and should be taken into account in studies of resolved galaxy properties and their evolution with redshift.

The Ancient Globular Clusters of NGC 1291

We present a new catalog of 81 ancient globular clusters (GCs) in the early-type spiral (SB0/a) galaxy NGC 1291. Candidates have been selected from B, V, and I band images taken with the Hubble Space Telescope, which also reveal 17 younger (τ ≲ few × 100 Myr) clusters. The luminosity function shows a peaked shape similar to that found for GC systems in other spiral and elliptical galaxies. The ancient clusters have a bimodal color distribution, with approximately 65% (35%) of the population having blue (red) colors. The red, presumably metal-rich, GCs are more centrally concentrated, as expected for a bulge population; while the blue, presumably metal-poor, GCs are more broadly distributed, consistent with expectations of a halo population. The specific frequency of GCs in NGC 1291 is higher than found previously in most spiral galaxies. However, if we consider just the blue subpopulation, we find S N,blue = 0.50 ± 0.06, quite similar to that found for other spirals. This result supports the hypothesis of a universal population of halo GCs in spirals. The fraction of red GCs in NGC 1291, when compared with those found in other galaxies, suggests that these correlate with host galaxy type rather than with host galaxy luminosity.

Three-dimensional episodic model of star formation in galaxies in the presence of dissipation

ABSTRACT The oscillatory model of star formation in giant and dwarf galaxies have been studied through a dynamical open system. In addition to various dynamical processes involving fractional masses of hot, warm, and cold gases, the system is subjected to dissipative processes e.g. outflow from the gaseous component caused by supernovae explosion and subsequent ram pressure stripping within the oscillation period. This is more realistic than a previous model which was considered conservative. The present episodic model has been found to be unimodal in general contrary to discrete episodes of star formation of decreasing amplitudes as found for closed systems. The duty cycles under various parametric conditions derived, vary in the range (2.0–40.0) × 107 yr for giant galaxies contrary to longer time, for example 9.0 × 107–1.0 × 109 yr for dwarf galaxies. This might be due to the low production rate of supernova in dwarf galaxies which reduces the evaporation rate of cold gas into hot gas making cold gas available for continuing the cycle for a longer time. The duty cycles have increased in both cases compared to the previous model by an order of one for giant galaxies and order of two for dwarf galaxies depending on the degree of dissipation. This might be due to the unimodal pattern of star formation which prevails for longer time in the late phase of galaxy evolution. Under very special parametric conditions limit cycles may occur i.e. star formation in discrete episodes, may occur involving one or more stable attractors especially in early-type dwarf and giant galaxies. Tendency of formation of multiple attractors are more likely in early-type giant spiral galaxies when the rate of dissipation is very slow.

Co-evolution of nuclear rings, bars and the central intensity ratio of their host galaxies

Using a sample of 13 early-type spiral galaxies hosting nuclear rings, we report remarkable correlations between the properties of the nuclear rings and the central intensity ratio (CIR) of their host galaxies. The CIR, a function of intensity of light within the central 1.5 and 3 arcsec region, is found to be a vital parameter in galaxy evolution, as it shares strong correlations with many structural and dynamical properties of early-type galaxies, including mass of the central supermassive black hole (SMBH). We use archival HST images for aperture photometry at the centre of the galaxy image to compute the CIR. We observe that the relative sizes of nuclear rings and ring cluster surface densities strongly correlate with the CIR. These correlations suggest reduced star formation in the centres of galaxies hosting small and dense nuclear rings. This scenario appears to be a consequence of strong bars as advocated by the significant connection observed between the CIR and bar strengths. In addition, we observe that the CIR is closely related with the integrated properties of the stellar population in the nuclear rings, associating the rings hosting older and less massive star clusters with low values of CIR. Thus, the CIR can serve as a crucial parameter in unfolding the coupled evolution of bars and rings as it is intimately connected with both their properties.

A New Perspective on the Large-scale Tidal Effect on the Galaxy Luminosity and Morphology

Abstract We study the mean tidal coherence of galaxy environments as a function of intrinsic luminosity determined by the absolute r-band magnitude. The tidal coherence of a galaxy environment is estimated as the cosine of the angle between two minor eigenvectors of the tidal field smoothed at the scales of 2 and 30 h −1 Mpc, respectively, centered on each of the local galaxies from the Sloan Digital Sky Data Release 10. Creating four luminosity-selected samples of the Sloan galaxies, we control them to have identical density distributions in order to nullify the dominant effect of the local density. The samples containing more luminous wall and field galaxies were found to yield lower mean values of the tidal coherence, which is a trend that turns out to be robust against the variation of the smoothing scales. At a fixed morphology, the same trend is found for the late-type spiral and lenticular galaxies in both of the field and wall environments. The early-type spiral field galaxies show no significant dependence on the tidal coherence, while both of the least and most luminous elliptical wall galaxies are found to dwell in the regions with highest tidal coherence.

Detection of Intrinsic Spin Alignments in Isolated Spiral Pairs

Abstract Observational evidence for intrinsic galaxy alignments in isolated spiral pairs is presented. From the catalog of the galaxy groups identified by Tempel et al. in the flux-limited galaxy sample of the Sloan Digital Sky Survey Data Release 10, we select those groups consisting only of two spiral galaxies as isolated spiral pairs and investigate if and how strongly the spin axes of their two spiral members are aligned with each other. We detect a clear signal of intrinsic spin alignment in isolated spiral pairs, which leads to the rejection of the null hypothesis at the 99.9999% confidence level via the Rayleigh test. It is also found that those isolated pairs comprising two early-type spiral galaxies exhibit the strongest signal of intrinsic spin alignment and that the strength of the alignment signal depends on the angular separation distance as well as on the luminosity ratio of the member galaxies. Using the dark matter halos consisting of only two subhalos resolved in the EAGLE hydrodynamic simulations, we repeat the same analysis but fail to find any alignment tendency between the spin angular momentum vectors of the stellar components of the subhalos, which is in tension with the observational result. Several possible sources of this apparent inconsistency between the observational and the numerical results are discussed.

On the interdependence of galaxy morphology, star formation and environment in massive galaxies in the nearby Universe

Using multi-wavelength data, from UV-optical-near-mid IR, for $\sim$6000 galaxies in the local Universe, we study the dependence of star formation on the morphological T-types for massive galaxies ($\log M_*/M_\odot \geq 10$). We find that, early-type spirals (Sa-Sbc) and S0s predominate in the green valley, which is a transition zone between the star forming and quenched regions. Within the early-type spirals, as we move from Sa to Sbc spirals the fraction of green valley and quenched galaxies decreases, indicating the important role of the bulge in the quenching of galaxies. The fraction of early-type spirals decreases as we enter the green valley from the blue cloud, which coincides with the increase in the fraction of S0s. This points towards the morphological transformation of early-type spiral galaxies into S0s which can happen due to environmental effects such as ram-pressure stripping, galaxy harassment, or tidal interactions. We also find a second population of S0s which are actively star-forming and are present in all environments. Since morphological T-type, specific star formation rate (sSFR), and environmental density are all correlated with each other, we compute the partial correlation coefficient for each pair of parameters while keeping the third parameter as a control variable. We find that morphology most strongly correlates with sSFR, independent of the environment, while the other two correlations (morphology-density and sSFR-environment) are weaker. Thus, we conclude that, for massive galaxies in the local Universe, the physical processes that shape their morphology are also the ones that determine their star-forming state.

The incidence of nuclear activity in galaxy pairs with different morphologies (E+E), (E+S) and (S+S)

We analysed 385 galactic spectra from the Sloan Digital Sky Survey Data Release 7 (SDSS-DR7) that belong to the catalog of isolated pairs of galaxies by Karachentsev. The spectra corresponds to physical pairs of galaxies as defined by V $\leq$ 1200 Km/s and a pair separation $\leq$ 100 kpc. We search for the incidence of nuclear activity, both thermal (star-forming) and non-thermal -Active Galactic Nuclei (AGN). After a careful extraction of the nuclear spectra, we use diagnostic diagrams and find that the incidence of AGN activity is 48 \% in the paired galaxies with emission lines and 40\% for the total sample (as compared to $\sim$ 43 \% and 41\% respectively in a sample of isolated galaxies). These results remain after dissecting the effects of morphological type and galactic stellar mass (with only a small, non significant, enhancement of the AGN fraction in pairs of objects). These results suggest that weak interactions are not necessary or sufficient to trigger low-luminosity AGN. Since the fraction of AGN is predominant in early type spiral galaxies, we conclude that the role of a bulge, and a large gas reservoir are both essential for the triggering of nuclear activity. The most striking result is that type 1 galaxies are almost absent from the AGN sample. This result is in conflict with the Unified Model, and suggests that high accretion rates are essential to form the Broad Line Region in active galaxies.

Studies of the stellar populations of galaxies using two-color diagrams

Variations in the photometric parameters of stellar systems as a function of their evolution and the stellar populations comprising them are investigated. A set of seven evolutionary models with an exponential decrease in the star-formation rate and 672 models with a secondary burst of star formation are considered. The occurrence of a secondary burst of star formation can shift the position of a stellar system on two-color diagrams to the right or left of the normal color sequence for galaxies and the extinction line. This makes it possible to estimate the composition of the stellar population of a galaxy with a nonmonotonic star formation history from its position on two-color diagrams. Surface photometry in both the optical (UBVRI) and near-IR (JHK) is used to study the stellar populations and star-formation histories in the structural components (nucleus, bulge, disk, spiral arms, bar, ring) of 26 galaxies of various morphological types (from S0 to Sd). Components (nucleus, bulge, bar) with color characteristics corresponding to stellar systems with secondary bursts of star formation are indicated in 10 of the 26 galaxies. The parameters of these secondary bursts are estimated. Five of the 10 galaxies with complex star-formation histories display clear structural perturbations. Appreciable differences in the photometric characteristics of relatively red early-type galaxies (S0-Sb) and relatively blue later-type galaxies (Sb-Sd) have been found. Galaxies of both early and late types are encountered among the Sb-galaxies. Lenticular galaxies do not display different photometric characteristics from early-type spiral galaxies.

A comprehensive photometric study of circumnuclear star-forming rings - I. The sample

We present photometry in U, B, V, R and I continuum bands and in H$\alpha$ and H$\beta$ emission lines for a sample of 336 circumnuclear star forming regions (CNSFR) located in early type spiral galaxies with different levels of activity in their nuclei. They are nearby galaxies, with distances less than 100 Mpc, 60\% of which are considered as interacting objects. This survey of 20 nuclear rings aims to provide insight into their star formation properties as age, stellar population and star formation rate. Extinction corrected H$\alpha$ luminosities range from $1.3\times 10^{38}$ to $4\times 10^{41} erg s^{-1}$, with most of the regions showing values between 39.5 $\leq log L(H\alpha) \leq$ 40, which implies masses for the ionizing clusters higher than $2\times 10^{5} M_\odot $. H$\alpha$ and H$\beta$ images have allowed us to obtain an accurate measure of extinction. We have found an average value of A$_V$ = 1.85 magnitudes. (U-B) colour follows a two maximum distribution around (U-B)$ \simeq$ -0.7, and -0.3; (R-I) also presents a bimodal behaviour, with maximum values of 0.6 and 0.9. Reddest (U-B) and (R-I) regions appear in non-interacting galaxies. Reddest (R-I) regions lie in strongly barred galaxies. For a significant number of HII regions the observed colours and equivalent widths are not well reproduced by single burst evolutionary theoretical models.

Visiting two objects in the field of the ring galaxy HRG 2302

Aims. We investigate the nature of two galaxies that are located in the field of the ring galaxy HRG 2302. Methods. This study is based on direct BVRI imaging and long-slit spectrophotometric data in the range of 4000−9500 A obtained with the 1.6 m telescope of the Observatorio do Pico dos Dias, Brazil. The spectra were used to determine the radial velocity. Results. The primary objective of the retrieval of the photometric data was to identify the fine structures of objects H and I. In addition, we performed image processing and made a photometric analysis to obtain the integrated standard BVRI magnitudes. The contour maps show evidence of material connecting both galaxies, suggesting that they might be interacting close companions. We estimated redshifts of z = 0.0689 and z = 0.0692. The spectra of the two galaxies resemble those of an early-type galaxy. The fact that the objects have a small radial-velocity difference and the structures around object I suggest an ongoing tidal interaction between the two galaxies. Conclusions. The H-I system seems to be composed of two early-type spiral galaxies (S0/Sa). Galaxy I shows evidence of tidal perturbation: an off-centered bulge, some material extending along the NE direction, and structures that have been enhanced by image filtering procedures. There are some dwarf objects around it. Neither object shows evidence of nuclear activity.

The relation between the gas, dust and total mass in edge-on spiral galaxies

AbstractEach component of a galaxy plays its own unique role in regulating the galaxy's evolution. In order to understand how galaxies form and evolve, it is therefore crucial to study the distribution and properties of each of the various components, and the links between them, both radially and vertically. The latter is only possible in edge-on systems. We present the HEROES project, which aims to investigate the 3D structure of the interstellar gas, dust, stars and dark matter in a sample of 7 massive early-type spiral galaxies based on a multi-wavelength data set including optical, NIR, FIR and radio data.

Regrowth of stellar discs in mature galaxies: the two-component nature of NGC 7217 revisited with VIRUS-W

Previous studies have reported the existence of two counter-rotating stellar disks in the early-type spiral galaxy NGC7217. We have obtained high-resolution optical spectroscopic data (R ~ 9000) with the new fiber-based Integral Field Unit instrument VIRUS-W at the 2.7m telescope of the McDonald Observatory in Texas. Our analysis confirms the existence of two components. However, we find them to be co-rotating. The first component is the more luminous (~ 77% of the total light), has the higher velocity dispersion (~ 170 km/s) and rotates relatively slowly (projected $v_{max}$ = 50 km/s). The lower luminosity second component, (~ 23% of the total light), has a low velocity dispersion (~ 20 km/s) and rotates quickly (projected $v_{max}$ = 150 km/s). The difference in the kinematics of the two stellar components allows us to perform a kinematic decomposition and to measure the strengths of their Mg and Fe Lick indices separately. The rotational velocities and dispersions of the less luminous and faster component are very similar to those of the interstellar gas as measured from the [OIII] emission. Morphological evidence of active star formation in this component further suggests that NGC7217 may be in the process of (re)growing a disk inside a more massive and higher dispersion stellar halo. The kinematically cold and regular structure of the gas disk in combination with the central almost dust-free morphology allows us to compare the dynamical mass inside of the central 500pc with predictions from a stellar population analysis. We find agreement between the two if a Kroupa stellar initial mass function is assumed.

The thickness of stellar disks in early-type galaxies

We suggest and verify a new photometric method enabling derivation of relative thickness of a galactic disk from two-dimensional surface-brightness distribution of the galaxy in the plane of the sky. The method is applied to images of 45 early-type (S0-Sb) galaxies with known radial exponential or double-exponential (with a flatter outer profile) surface-brightness distributions. The data in the r-band have been retrieved from the SDSS archive. Statistics of the estimated relative thicknesses of the stellar disks of early-type disk galaxies shows the following features. The disks of lenticular and early-type spiral galaxies have similar thicknesses. The presence of a bar results in only a slight marginal increase of the thickness. However, we have found a substantial difference between the thicknesses of the disks with a single-scaled exponential brightness profile and the disks that represent the inner segments of the Type III (antitruncated) profiles. The disks are significantly thicker in the former subsample than in the latter one. This may provide evidence for a surface-brightness distribution of a single-scaled exponential disk to be formed due to viscosity effects acting over the entire period of star formation in the disk.

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.

The link between the baryonic mass distribution and the rotation curve shape

The observed rotation curves of disc galaxies, ranging from late-type dwarf galaxies to early-type spirals, can be fit remarkably well simply by scaling up the contributions of the stellar and HI discs. This `baryonic scaling model' can explain the full breadth of observed rotation curves with only two free parameters. For a small fraction of galaxies, in particular early-type spiral galaxies, HI scaling appears to fail in the outer parts, possibly due to observational effects or ionization of the HI. The overall success of the baryonic scaling model suggests that the well-known global coupling between the baryonic mass of a galaxy and its rotation velocity (known as the baryonic Tully-Fisher relation), applies at a more local level as well, and it seems to imply a link between the baryonic mass distribution and the distribution of total mass (including dark matter).

ULTRAVIOLET COLOR-COLOR RELATION OF EARLY-TYPE GALAXIES AT 0.05 < z < 0.12

We present the ultraviolet (UV) color-color relation of early-type galaxies (ETGs) in the nearby universe (0.05 < z < 0.12) to investigate the properties of hot stellar populations responsible for the UV excess (UVX). The initial sample of ETGs is selected by the spectroscopic redshift and the morphology parameter from the Sloan Digital Sky Survey (SDSS) DR7, and then cross-matched with the Galaxy Evolution Explorer (GALEX) Far-UV (FUV) and Near-UV (NUV) GR6 data. The cross-matched ETG sample is further classified by their emission line characteristics in the optical spectra into quiescent, star-forming, and AGN categories. Contaminations from early-type spiral galaxies, mergers, and morphologically disturbed galaxies are removed by visual inspection. By drawing the FUV - NUV (as a measure of UV spectral shape) vs. FUV - r (as a measure of UVX strength) diagram for the final sample of ~3700 quiescent ETGs, we find that the "old and dead" ETGs consist of a well-defined sequence in UV colors, the "UV red sequence", so that the stronger UVX galaxies should have a harder UV spectral shape systematically. However, the observed UV spectral slope is too steep to be reproduced by the canonical stellar population models in which the UV flux is mainly controlled by age or metallicity parameters. Moreover, 2 mag of color spreads both in FUV - NUV and FUV - r appear to be ubiquitous among any subsets in distance or luminosity. This implies that the UVX in ETGs could be driven by yet another parameter which might be even more influential than age or metallicity.