ABSTRACT
Dwarfs are the largest population of galaxies in number in the nearby Universe. Deep spectroscopic data are still missing to obtain a better understanding of their formation and evolution ...processes. This study shows the results obtained from a spectroscopic campaign in the Perseus cluster. We have obtained 963 new galaxy spectra. We have measured the recessional velocity of the galaxies by using a cross-correlation technique. These data have been used to obtain the cluster membership, the dynamics of the galaxies, and the spectroscopic luminosity function (LF) of the cluster. The cluster membership was obtained by using the peak + gap technique, reporting a total of 403 galaxies as cluster members within 1.4r200. The mean velocity and velocity dispersion of the cluster galaxies are Vc = 5258 km s−1 and σc = 1040 km s−1, respectively. We obtained M200 = 1.2 × 1015 M⊙ and r200 = 2.2 Mpc for this cluster. The clusters members were classified blue and red according to their g − r stellar colour. The velocity dispersion of these two families of galaxies is different, indicating that the blue galaxies can be classified as recently accreted into the cluster. We present the spectroscopic galaxy LF of the cluster. This function turned to be flat: α = 0.99 ± 0.06. In addition, blue and red galaxies show similar densities in the faint end of the LF. This indicates that Perseus does not have a population of red dwarf galaxias as large as other nearby clusters. We have compared the LF of the Perseus cluster with other spectroscopic LFs of nearby clusters and those from cosmological simulations. This comparison shows that the spectroscopic LF of nearby galaxy cluster is far from universal.
Abstract
Galaxies in clusters are strongly affected by their environment. They evolve according to several physical mechanisms that are active in clusters. Their efficiency can strongly depend on the ...orbital configuration of the galaxies. Our aim is to analyse the orbits of the galaxies in the cluster Abell 85, based on the study of the galaxy velocity anisotropy parameter. We have solved the Jeans equation under the assumption that the galaxies in A 85 are collisionless objects, within the spherically symmetric gravitational potential of the virialized cluster. The mass of the cluster was estimated with X-ray and caustic analyses. We find that the anisotropy profile of the full galaxy population in A 85 is an increasing monotonic function of the distance from the cluster centre: on average, galaxies in the central region (r/r
200 < 0.3) are on isotropic orbits, while galaxies in the outer regions are on radial orbits. We also find that the orbital properties of the galaxies strongly depend on their stellar colour. In particular, blue galaxies are on less radial orbits than red galaxies. The different families of cluster galaxies considered here have the pseudo phase-space density profiles Q(r) and Q
r
(r) consistent with the profiles expected in virialized dark matter haloes in N-body simulations. This result suggests that the galaxies in A 85 have reached dynamical equilibrium within the cluster potential. Our results indicate that the origin of the blue and red colours of the different galaxy populations is the different orbital shape rather than the accretion time.
Abstract
Our aim is to understand the role of the environment in the quenching of star formation of galaxies located in the infall cluster region of Abell 85 (A85). This is achieved by studying the ...post-starburst galaxy population as tracer of recent quenching. By measuring the equivalent width (EW) of the O ii and Hδ spectral lines, we classify the galaxies into three groups: passive (PAS), emission line (EL), and post-starburst (PSB) galaxies. The PSB galaxy population represents ${\sim } 4.5\hbox{ per cent}$ of the full sample. Dwarf galaxies (Mr > −18.0) account for ${\sim } 70 {\rm -} 80\hbox{ per cent}$ of PSBs, which indicates that most of the galaxies undergoing recent quenching are low-mass objects. Independently of the environment, PSB galaxies are disc-like objects with g − r colour between the blue ELs and the red PAS ones. The PSB and EL galaxies in low-density environments show similar luminosities and local galaxy densities. The dynamics and local galaxy density of the PSB population in high-density environments are shared with PAS galaxies. However, PSB galaxies inside A85 are at shorter clustercentric radius than PAS and EL ones. The value of the EW(Hδ) is larger for those PSBs closer to the cluster centre. We propose two different physical mechanisms producing PSB galaxies depending on the environment. In low-density environments, gas-rich minor mergers or accretions could produce the PSB galaxies. For high-density environments like A85, PSBs would be produced by the removal of the gas reservoirs of EL galaxies by ram-pressure stripping when they pass near the cluster centre.
We present a new deep spectroscopic catalogue for Abell 85, within 3.0 × 2.6 Mpc2 and down to
$M_{r} \sim M_{r}^{\ast } +6$
. Using the Visible Multi-Object Spectrograph at the Very Large Telescope ...and the AutoFiber 2 at the William Herschel Telescope, we obtained almost 1430 new redshifts for galaxies with m
r
≤ 21 mag and 〈μ
e,r
〉 ≤ 24 mag arcsec−2. These redshifts, together with Sloan Digital Sky Survey Data Release 6 and NASA/IPAC Extragaalctic Database spectroscopic information, result in 460 confirmed cluster members. This data set allows the study of the luminosity function (LF) of the cluster galaxies covering three orders of magnitudes in luminosities. The total and radial LFs are best modelled by a double Schechter function. The normalized LFs show that their bright (M
r
≤ −21.5) and faint (M
r
≥ −18.0) ends are independent of clustercentric distance and similar to the field LFs unlike the intermediate luminosity range (−21.5 ≤ M
r
≤ −18.0). Similar results are found for the LFs of the dominant types of galaxies: red, passive, virialized and early-infall members. On the contrary, the LFs of blue, star forming, non-virialized and recent-infall galaxies are well described by a single Schechter function. These populations contribute to a small fraction of the galaxy density in the innermost cluster region. However, in the outskirts of the cluster, they have similar densities to red, passive, virialized and early-infall members at the LF faint end. These results confirm a clear dependence of the colour and star formation of Abell 85 members in the cluster centric distance.
Abstract
We present a new deep determination of the spectroscopic luminosity function (LF) within the virial radius of the nearby and massive Abell 85 (A85) cluster down to the dwarf regime (M* + 6) ...using Very Large Telescope/Visible Multi-Object Spectrograph (VLT/VIMOS) spectra for ∼2000 galaxies with mr ≤ 21 mag and 〈μe,r〉 ≤ 24 mag arcsec−2. The resulting LF from 438 cluster members is best modelled by a double Schechter function due to the presence of a statistically significant upturn at the faint end. The amplitude of this upturn ($\alpha _{{\rm f}} = -1.58^{+0.19}_{-0.15}$), however, is much smaller than that of the Sloan Digital Sky Survey (SDSS) composite photometric cluster LF by Popesso et al., αf ∼ −2. The faint-end slope of the LF in A85 is consistent, within the uncertainties, with that of the field. The red galaxy population dominates the LF at low luminosities, and is the main factor responsible for the upturn. The fact that the slopes of the spectroscopic LFs in the field and in a cluster as massive as A85 are similar suggests that the cluster environment does not play a major role in determining the abundance of low-mass galaxies.
We present the study of the colour–magnitude diagram of the cluster Abell 2151 (A 2151), with a particular focus on the low-mass end. The deep spectroscopy with AF2/WYFFOS@WHT and the caustic method ...enable us to obtain 360 members within 1.3 R
200 and absolute magnitude
$M_r \lesssim M_r^{\ast }+6$
. This nearby cluster shows a well defined red sequence up to M
r
∼ −18.5; at fainter magnitudes only 36 per cent of the galaxies lie on the extrapolation of the red sequence. We compare the red sequences of A 2151 and Abell 85, which is another nearby cluster with similar spectroscopic data, but with different mass and dynamical state. Both clusters show similar red sequences at the bright end (M
r
≤ −19.5), whereas large differences appear at the faint end. This result suggests that the reddening of bright galaxies is independent of environment, unlike the dwarf population (M
r
≥ −18.0).
Polarization variability is one of the most ubiquitous characteristic of blazars. Near infrared (NIR)polarization measurements of blazars are not common, contrary to the optical ones. Nonetheless, ...the NIR regime can be essential to understand correlated or non-correlated behaviour between the optical and radio energy ranges. In this work, we report on NIR polarimetry measurements of a sample of 28 blazars, collected with LIRIS at WHT/La Palma in several campaigns during 2011. The majority of the blazars were observed more than one epoch using two filters (J and Ks). Here we present preliminary results for few selected targets.
Our aim is to understand the role of the environment in the quenching of star formation of galaxies located in the infall cluster region of Abell 85 (A85). This is achieved by studying the ...post-starburst galaxy population as tracer of recent quenching. By measuring the equivalent width (EW) of the OII and Hdelta spectral lines, we classify the galaxies in three groups: passive (PAS), emission line (EL), and post-starburst (PSB) galaxies. The PSB galaxy population represents about 4.5% of the full sample. Dwarf galaxies (Mr > -18.0) account for about 70 - 80% of PSBs, which indicates that most of the galaxies undergoing recent quenching are low-mass objects. Independently of the environment, PSB galaxies are disk-like objects with g - r colour between the blue ELs and the red PAS ones. The PSB and EL galaxies in low-density environments show similar luminosities and local galaxy densities. The dynamics and local galaxy density of the PSB population in high density environments are shared with PAS galaxies. However, PSB galaxies inside A85 are at shorter clustercentric radius than PAS and EL ones. The value of the EW(Hdelta) is larger for those PSBs closer to the cluster centre. We propose two different physical mechanisms producing PSB galaxies depending on the environment. In low density environments, gas-rich minor mergers or accretions could produce the PSB galaxies. For high density environments like A85, PSBs would be produced by the removal of the gas reservoirs of EL galaxies by ram-pressure stripping when they pass near to the cluster centre.
Galaxies in clusters are strongly affected by their environment. They evolve according to several physical mechanisms that are active in clusters. Their efficiency can strongly depend on the orbital ...configuration of the galaxies. Our aim is to analyse the orbits of the galaxies in the cluster Abell 85, based on the study of the galaxy velocity anisotropy parameter. We have solved the Jeans equation under the assumption that the galaxies in A85 are collisionless objects, within the spherically symmetric gravitational potential of the virialized cluster. The mass of the cluster was estimated with X-ray and caustic analyses. We find that the anisotropy profile of the full galaxy population in A85 is an increasing monotonic function of the distance from the cluster centre: on average, galaxies in the central region (r/r200 < 0.3) are on isotropic orbits, while galaxies in the outer regions are on radial orbits. We also find that the orbital properties of the galaxies strongly depend on their stellar colour. In particular, blue galaxies are on less radial orbits than red galaxies. The different families of cluster galaxies considered here have the pseudo phase-space density profiles Q(r) and Qr(r) consistent with the profiles expected in virialized dark matter halos in \(N\)-body simulations. This result suggests that the galaxies in A85 have reached dynamical equilibrium within the cluster potential. Our results indicate that the origin of the blue and red colour of the different galaxy populations is the different orbital shape rather than the accretion time.
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