In this work, we study the evolution with redshift of the colour-magnitude relation (CMR) of early-type galaxies. This evolution is analyzed through cosmological numerical simulations from z = 2 to z = 0. The preliminary results shown here represent the starting point of a study aimed at identifying the processes that originated the observed CMR of early-type galaxies at z = 0.
Using deep, high-spatial resolution imaging from the HST ACS Coma Cluster Treasury Survey, we determine colour profiles of early-type galaxies in the Coma cluster. From 176 galaxies brighter than $M_\mathrm{F814W(AB)} = -15$ mag that are either spectroscopically confirmed members of Coma or identified by eye as likely members from their low surface brightness, data are provided for 142 early-type galaxies. Typically, colour profiles are linear against $\log(R)$, sometimes with a nuclear region of distinct, often bluer colour associated with nuclear clusters. Colour gradients are determined for…
Early-type dwarf galaxies are not simply featureless, old objects, but were found to be much more diverse, hosting substructures and a variety of stellar population properties. To explore the stellar content of faint early-type galaxies, and to investigate in particular those with recent central star formation, we study colours and colour gradients within one effective radius in optical (g-r) and near-infrared (i-H) bands for 120 Virgo cluster early types with -19 mag < $M_{r}$ < -16 mag. Twelve galaxies turn out to have blue cores, when defined as g-r colour gradients larger than 0.10 mag/$R_…
Recent studies have shown that the observed colour distributions of Type Ia SNe (SNIa) are well-described by a combination of distributions from dust and intrinsic colour. Here we present a new forward-modeling fitting method (Dust2Dust) to measure the parent dust and colour distributions, including their dependence on host-galaxy mass. At each fit step, the SNIa selection efficiency is determined from a large simulated sample that is re-weighted to reflect the proposed distributions. We use five separate metrics to constrain the Dust2Dust parameters: distribution of fitted light-curve colour …
Context. Absorption line indices are widely used to determine the stellar population parameters such as age and metallicity of galaxies, but it is not easy to obtain the line indices of some distant galaxies that have colours available. Aims. This paper investigates the correlations between absorption line indices and colours. Methods. A few statistical fitting methods are mainly used, via both the observational data of Sloan Digital Sky Survey and a widely used theoretical stellar population model. Results. Some correlations between widely used absorption line indices and ugriz colours are fo…
We present GALEX far (FUV) and near (NUV) ultraviolet imaging of 34 nearby early-type galaxies from the SAURON representative sample of 48 E/S0 galaxies, all of which have ground-based optical imaging from the MDM Observatory. The surface brightness profiles of nine galaxies show regions with blue UV-optical colours suggesting recent star formation. Five of these show blue integrated UV-optical colours that set them aside in the NUV integrated colour-magnitude relation. They also have other properties confirming they have had recent star formation, in particular H_beta absorption higher than e…
We explore the internal structure of red sequence galaxies in the Coma cluster across a wide range of luminosities ($-17>M_g>-22$) and cluster-centric radii ($0<r_{\rm{cluster}}<1.3 r_{200}$). We present the 2D bulge-disc decomposition of galaxies in deep Canada-France-Hawaii Telescope $u,g,i$ imaging using GALFIT. Rigorous filtering is applied to identify an analysis sample of 200 galaxies which are well described by an `archetypal' S0 structure (central bulge + outer disc). We consider internal bulge and/or disc colour gradients by allowing component sizes to vary between bands. Gradients ar…
Galaxy spectral energy distributions (SEDs) remain among the most challenging yet informative quantities to reproduce in simulations due to the large and complex mixture of physical processes that shape the radiation output of a galaxy. With the increasing number of surveys utilising broadband colours as part of their target selection criteria, the production of realistic SEDs in simulations is necessary for assisting in survey design and interpretation of observations. The recent success in reproducing the observed luminosity functions (LF) from far-UV to far-IR, using the state-of-the-art se…
The galaxy population is strongly bimodal in both colour and morphology, and the two measures correlate strongly, with most blue galaxies being late-types (spirals) and most early-types, typically ellipticals, being red. This observation has led to the use of colour as a convenient selection criteria to make samples which are then labelled by morphology. Such use of colour as a proxy for morphology results in necessarily impure and incomplete samples. In this paper, we make use of the morphological labels produced by Galaxy Zoo to measure how incomplete and impure such samples are, considering…
We explore the evolution of the statistical distribution of galaxy morphological properties and colours over the redshift range $0.5<z<1$, combining high-quality imaging data from the CFHT Legacy Survey with the large number of redshifts and extended photometry from the VIPERS survey. Galaxy structural parameters are measured by fitting Sérsic profiles to $i$-band images and then combined with absolute magnitudes, colours and redshifts, to trace the evolution in a multi-parameter space. We analyse, using a new method, the combination of colours and structural parameters of early- and late-type…
We present a study of the cold gas contents of the Atlas3D early-type galaxies, in the context of their optical colours, near-UV colours, and Hβ absorption line strengths. Early-type (elliptical and lenticular) galaxies are not as gas-poor as previously thought, and at least 40% of local early-type galaxies are now known to contain molecular and/or atomic gas. This cold gas offers the opportunity to study recent galaxy evolution through the processes of cold gas acquisition, consumption (star formation), and removal. Molecular and atomic gas detection rates range from 10% to 34% in red sequenc…
State-of-the-art cosmological hydrodynamical simulations have star particles with typical mass between $\sim 10^8$ and $\sim 10^3$ M$_{\odot}$ according to resolution, and treat them as simple stellar populations. On the other hand, observations in nearby galaxies resolve individual stars and provide us with single star properties. An accurate and fair comparison between predictions from simulations and observations is a crucial task. We introduce a novel approach to consistently populate star particles with stars. We developed a technique to generate a theoretical catalogue of mock stars whos…
The properties of isolated galaxies are mainly driven by intrinsic evolution and not by the external influence of their environments. Therefore the isolated galaxy sample may be considered as a reference sample to study different environmental effects. We made detailed comparisons between the near-infrared (2MASS) and optical (SDSS) colours of the 2MASS XSC selected sample of isolated 2MIG galaxies and with other objects from the wide range of denser environments (field, groups/clusters, triplets and pairs). We found that early type galaxies show similar (J-H)rest and (g-r)rest colours practic…
The transformation of late-type galaxies has been suggested as the origin of early-type dwarf galaxies in galaxy clusters. Venhola et al. analysed correlations between colour and surface brightness for galaxies in the Fornax cluster binned by luminosity or stellar mass. In the bins with $M_\star<10^8 {\rm M}_\odot$, the authors identified a correlation of redness with fainter surface brightness and interpreted it as a consequence of the quenching of star formation by ram pressure stripping in the dwarf galaxies. We carry out a corresponding analysis for the Virgo cluster and find great similar…
We present the effective temperatures ($T_{\rm eff}$), metallicities, and colours in SDSS, 2MASS, and WISE filters, of a sample of 3834 late-K and early-M dwarfs selected from the Sloan Digital Sky Survey APOGEE spectroscopic survey ASPCAP catalog. We confirm that ASPCAP $T_{\rm eff}$ values between 3550 K$<T_{\rm eff}<$4200 K are accurate to $\sim$100 K compared to interferometric $T_{\rm eff}$ values. In that same $T_{\rm eff}$ range, ASPCAP metallicities are accurate to 0.18 dex between $-1.0<$[M/H]$<0.2$. For these cool dwarfs, nearly every colour is sensitive to both $T_{\rm eff}$ and met…
We extend our initial study of the connection between the UV colour of galaxies and both the inferred stellar mass-to-light ratio, $Υ_*$, and a mass-to-light ratio referenced to Salpeter initial mass function (IMF) models of the same age and metallicity, $Υ_*/Υ_{Sal}$, using new UV magnitude measurements for a much larger sample of early-type galaxies, ETGs, with dynamically determined mass-to-light ratios. We confirm the principal empirical finding of our first study, a strong correlation between the GALEX FUV-NUV colour and $Υ_*$. We show that this finding is not the result of spectral disto…
Using GALEX, UVOT and optical photometry, we explore the prevalence and strength of the UV-upturn in the spectra of quiescent early type galaxies in several nearby clusters. Even for galaxies with completely passive optical colours, there is a large spread in vacuum UV colour consistent with almost all having some UV upturn component. Combining GALEX and UVOT data below 3000Å, we generate for the first time comparatively detailed UV SEDs for Coma cluster galaxies. Fitting the UV upturn component with a blackbody, twenty six of these show a range of characteristic temperatures (10000--21000K) f…
We constrain the light extinction properties of Milky Way dust. We investigated the correlations between dust column density as inferred from infrared data and the observed colours of celestial objects at cosmological distances with low levels of colour dispersion. Results derived using colours of quasars, brightest central galaxies, and luminous red galaxies are broadly consistent, indicating a proportionality constant between the reddening E(B-V)=A_B-A_V and the dust column density D^T (given in units of MJy/sr) of p=E(B-V)/D^T=0.02 and a reddening parameter R_V=A_V/E(B-V)=3 with fractional …
We investigate the nature of HI-rich galaxies from the ALFALFA and GASS surveys, which are defined as galaxies in the top 10th percentile in atomic gas fraction at a given stellar mass. We analyze outer (R>1.5 Re) stellar populations for a subset of face-on systems using optical g-r versus r-z colour/colour diagrams. The results are compared with those from control samples that are defined without regard to atomic gas content, but are matched in redshift, stellar mass and structural parameters. HI-rich early-type (C>2.6) and late-type (C<2.6) galaxies are studied separately. When compared to t…
We present a catalogue of 1715 early-type galaxies from the literature, spanning the luminosity range from faint dwarf spheroidal galaxies to giant elliptical galaxies. The aim of this catalogue is to be one of the most comprehensive and publicly available collections of data on early-type galaxies. The emphasis in this catalogue lies on dwarf elliptical galaxies, for which some samples with detailed data have been published recently. For almost all of the early-type galaxies included in it, this catalogue contains data on their locations, distances, redshifts, half-light radii, the masses of …
We present an extension of our previous research on the early-type galaxy population of the Antlia cluster (d ~ 35 Mpc), achieving a total coverage of ~ 2.6 deg x deg and performing surface photometry for ~300 galaxies, 130 of which are new uncatalogued ones. Such new galaxies mainly fall in the low surface brightness (LSB) regime, but there are also some lenticulars (S0) which support the existence of unique functions that connect bright and dwarf galaxies in the scaling relations. We analyse the projected spatial distribution of galaxies up to a distance of ~800 kpc from NGC 3268, the adopte…
We investigate the relation between kinematic morphology, intrinsic colour and stellar mass of galaxies in the EAGLE cosmological hydrodynamical simulation. We calculate the intrinsic u-r colours and measure the fraction of kinetic energy invested in ordered corotation of 3562 galaxies at z=0 with stellar masses larger than $10^{10}M_{\odot}$. We perform a visual inspection of gri-composite images and find that our kinematic morphology correlates strongly with visual morphology. EAGLE produces a galaxy population for which morphology is tightly correlated with the location in the colour- mass …
(Abridged) The formation of massive spheroidal galaxies is studied on a visually classified sample of 910 galaxies extracted from the ACS/HST images of the GOODS North and South fields (0.4<z<.5). Three key observables are considered: comoving number density, internal colour distribution; and the Kormendy relation. The comoving number density of the most massive galaxies is found not to change significantly with redshift. One quarter of the whole sample of early-types are photometrically classified as blue galaxies. On a volume-limited subset out to z<0.7, the average stellar mass of the blue …
We study the feedback from an AGN on stellar formation within its host galaxy, mainly using one high resolution numerical simulation of the jet propagation within the interstellar medium of an early-type galaxy. In particular, we show that in a realistic simulation where the jet propagates into a two-phase ISM, star formation can initially be slightly enhanced and then, on timescales of few million years, rapidly quenched, as a consequence both of the high temperatures attained and of the reduction of cloud mass (mainly due to Kelvin-Helmholtz instabilities). We then introduce a model of (prev…
We use the Hernández-Pérez $\&$ Bruzual (2013) HB13 stellar population synthesis models to study the rôle of interacting binary pairs as progenitors of EHB stars. We assemble a sample of 3417 Early Type Galaxies observed both in the optical (\textit{SDSS}-DR8) and the UV (\textit{GALEX}-GR6). The galaxies in our sample can be classified according to their position in the colour-colour diagram as UV weak or red sequence galaxies ($\sim 48\%$), UV strong or UVX galaxies ($\sim 9\%$), and recent star forming galaxies ($\sim 43\%$). Analysing this sample using the HB13 models for various choices o…
We present early science results from Deep Investigation of Neutral Gas Origins (DINGO), an HI survey using the Australian Square Kilometre Array Pathfinder (ASKAP). Using ASKAP sub-arrays available during its commissioning phase, DINGO early science data were taken over $\sim$ 60 deg$^{2}$ of the Galaxy And Mass Assembly (GAMA) 23 h region with 35.5 hr integration time. We make direct detections of six known and one new sources at $z < 0.01$. Using HI spectral stacking, we investigate the HI gas content of galaxies at $0.04 < z< 0.09$ for different galaxy colours. The results show that galaxy…
We analyse the star formation rates (SFRs), colours, and dust extinctions of galaxies in massive (10^12.5-10^13.5 Msun) haloes at z~2 in high-resolution, cosmological zoom-in simulations as part of the Feedback in Realistic Environments (FIRE) project. The simulations do not model feedback from active galactic nuclei (AGN) but reproduce well the observed relations between stellar and halo mass and between stellar mass and SFR. About half (a third) of the simulated massive galaxies (massive central galaxies) at z~2 have broad-band colours classifying them as 'quiescent', and the fraction of qui…
The success of Type Ia supernova (SN Ia) distance standardisation for cosmology relies on a single global linear relationship between their peak luminosity and colour, the $β$ parameter. However, there are several pieces of evidence and physical reasons to believe that this relation is not universal and may change within different subgroups, or even among individual objects. In this work, we allow $β$ to vary among subpopulations with different observed properties in the cosmological fits. Although the inferred cosmological parameters are consistent with previous studies that assume a single c…
We investigate the origin of the colour-magnitude relation (CMR) followed by early-type cluster galaxies by using a combination of cosmological N-body simulations of cluster of galaxies and a semi-analytic model of galaxy formation (Lagos, Cora & Padilla 2008). Results show good agreement between the general trend of the simulated and observed CMR. However, in many clusters, the most luminous galaxies depart from the linear fit to observed data displaying almost constant colours. With the aim of understanding this behaviour, we analyze the dependence with redshift of the stellar mass contribut…
CASCO: Cosmological and AStrophysical parameters from Cosmological simulations and Observations -- II. Constraining cosmology and astrophysical processes with early- and late-type galaxies
We constrain the spatial gradient of star formation history within galaxies using the colour gradients in NUV-u and u-i for a local spatially-resolved galaxy sample. By splitting each galaxy into an inner and an outer part, we find that most galaxies show negative gradients in these two colours. We first rule out dust extinction gradient and metallicity gradient as the dominant source for the colour gradient. Then using stellar population models, we explore variations in star formation history to explain the colour gradients. As shown by our earlier work, a two-phase SFH consisting of an early…
Using SDSS-DR7 and NASA/IPAC Extragalactic Database spectroscopic data, we identify 166 galaxies as members of the Ursa Major cluster with Mr < -13.5 mag. We morphological classify all galaxies by means of carefully inspecting g-, r-, i-band colour and monochromatic images. We show that the Ursa Major cluster is dominated by late-type galaxies, but also contains a significant number of early- type galaxies, particularly in the dwarf regime. We present further evidence for the existence of several subgroups in the cluster, consistent with previous findings. The early-type fraction is found to c…
The evolution of number density, size and intrinsic colour is determined for a volume-limited sample of visually classified early-type galaxies selected from the HST/ACS images of the GOODS North and South fields (version 2). The sample comprises 457 galaxies over 320 arcmin2 with stellar masses above 3E10 Msun in the redshift range 0.4<z<1.2. Our data allow a simultaneous study of number density, intrinsic colour distribution and size. We find that the most massive systems (>3E11 Msun) do not show any appreciable change in comoving number density or size in our data. Furthermore, when includi…
In this tutorial paper we summarize how the star formation (SF) history of a galactic region can be derived from the colour-magnitude diagram (CMD) of its resolved stars. The procedures to build synthetic CMDs and to exploit them to derive the SF histories (SFHs) are described, as well as the corresponding uncertainties. The SFHs of resolved dwarf galaxies of all morphological types, obtained from the application of the synthetic CMD method, are reviewed and discussed. In short: 1) Only early-type galaxies show evidence of long interruptions in the SF activity; late-type dwarfs present rather …
