208 research outputs found
From blue star-forming to red passive: galaxies in transition in different environments
Exploiting a mass complete (M_*>10^(10.25)M_sun) sample at 0.03<z<0.11 drawn
from the Padova Millennium Galaxy Group Catalog (PM2GC), we use the (U-B)_rf
color and morphologies to characterize galaxies, in particular those that show
signs of an ongoing or recent transformation of their star formation activity
and/or morphology - green galaxies, red passive late types, and blue
star-forming early types. Color fractions depend on mass and only for
M_*<10^(10.7)M_sun on environment. The incidence of red galaxies increases with
increasing mass, and, for M_*<10^(10.7)M_sun, decreases toward the group
outskirts and in binary and single galaxies. The relative abundance of green
and blue galaxies is independent of environment, and increases monotonically
with galaxy mass. We also inspect galaxy structural parameters, star-formation
properties, histories and ages and propose an evolutionary scenario for the
different subpopulations. Color transformations are due to a reduction and
suppression of SFR in both bulges and disks which does not noticeably affect
galaxy structure. Morphological transitions are linked to an enhanced
bulge-to-disk ratio due to the removal of the disk, not to an increase of the
bulge. Our modeling suggests that green colors might be due to star formation
histories declining with long timescales, as an alternative scenario to the
classical "quenching" processes. Our results suggest that galaxy
transformations in star formation activity and morphology depend neither on
environment nor on being a satellite or the most massive galaxy of a halo. The
only environmental dependence we find is the higher fast quenching efficiency
in groups giving origin to post-starburst signatures.Comment: 20 pages, 12 figures, accepted for publication in Ap
The star formation history of galaxies: the role of galaxy mass, morphology and environment
We analyze the star formation history (SFH) of galaxies as a function of
present-day environment, galaxy stellar mass and morphology. The SFH is derived
by means of a non-parametric spectrophotometric model applied to individual
galaxies at z ~ 0.04- 0.1 in the WINGS clusters and the PM2GC field. The field
reconstructed evolution of the star formation rate density (SFRD) follows the
values observed at each redshift (Madau & Dickinson 2014), except at z > 2
where our estimate is ~ 1.7x higher than the high-z observed value. The slope
of the SFRD decline with time gets progressively steeper going from low mass to
high mass haloes. The decrease of the SFRD since z = 2 is due to 1) quenching -
50% of the SFRD in the field and 75% in clusters at z > 2 originated in
galaxies that are passive today - and 2) the fact that the average SFR of
today's star-forming galaxies has decreased with time. We quantify the
contribution to the SFRD(z) of galaxies of today's different masses and
morphologies. The current morphology correlates with the current star formation
activity but is irrelevant for the past stellar history. The average SFH
depends on galaxy mass, but galaxies of a given mass have different histories
depending on their environment. We conclude that the variation of the SFRD(z)
with environment is not driven by different distributions of galaxy masses and
morphologies in clusters and field, and must be due to an accelerated formation
in high mass haloes compared to low mass ones even for galaxies that will end
up having the same galaxy mass today.Comment: 16 pages, 10 figures. Published on MNRA
Superdense galaxies and the mass-size relation at low redshift
We search for massive and compact galaxies (superdense galaxies, hereafter
SDGs) at z=0.03-0.11 in the Padova-Millennium Galaxy and Group Catalogue, a
spectroscopically complete sample representative of the local Universe general
field population. We find that compact galaxies with radii and mass densities
comparable to high-z massive and passive galaxies represent 4.4% of all
galaxies with stellar masses above 3 X 10^10 M_sun, yielding a number density
of 4.3 X 10^-4 h^3 Mpc^-3. Most of them are S0s (70%) or ellipticals (23%), are
red and have intermediate-to-old stellar populations, with a median
luminosity-weighted age of 5.4 Gyr and a median mass-weighted age of 9.2 Gyr.
Their velocity dispersions and dynamical masses are consistent with the small
radii and high stellar mass estimates. Comparing with the WINGS sample of
cluster galaxies at similar redshifts, the fraction of superdense galaxies is
three times smaller in the field than in clusters, and cluster SDGs are on
average 4 Gyr older than field SDGs. We confirm the existence of a universal
trend of smaller radii for older luminosity-weighted ages at fixed galaxy mass.
On top of the well known dependence of stellar age on galaxy mass, the
luminosity-weighted age of galaxies depends on galaxy compactness at fixed
mass, and, for a fixed mass and radius, on environment. This effect needs to be
taken into account in order not to overestimate the evolution of galaxy sizes
from high- to low-z. Our results and hierarchical simulations suggest that a
significant fraction of the massive compact galaxies at high-z have evolved
into compact galaxies in galaxy clusters today. When stellar age and
environmental effects are taken into account, the average amount of size
evolution of individual galaxies between high- and low-z is mild, a factor
~1.6. (abridged)Comment: ApJ, in pres
The evolution of galaxy sizes
We present a study of galaxy sizes in the local Universe as a function of
galaxy environment, comparing clusters and the general field. Galaxies with
radii and masses comparable to high-z massive and compact galaxies represent
4.4% of all galaxies more massive than 3 X 10^{10} M_sun in the field. Such
galaxies are 3 times more frequent in clusters than in the field. Most of them
are early-type galaxies with intermediate to old stellar populations. There is
a trend of smaller radii for older luminosity-weighted ages at fixed galaxy
mass. We show the relation between size and luminosity-weighted age for
galaxies of different stellar masses and in different environments. We compare
with high-z data to quantify the evolution of galaxy sizes. We find that, once
the progenitor bias due to the relation between galaxy size and stellar age is
removed, the average amount of size evolution of individual galaxies between
high- and low-z is mild, of the order of a factor 1.6.Comment: to appear in the proceedings of the IAU S295: The intriguing life of
massive galaxies, editors D. Thomas, A. Pasquali & I. Ferrera
The importance of the local density in shaping the galaxy stellar mass functions
Exploiting the capabilities of four different surveys --- the
Padova-Millennium Galaxy and Group Catalogue (PM2GC), the WIde-field Nearby
Galaxy-cluster Survey (WINGS), the IMACS Cluster Building Survey (ICBS) and the
ESO Distant Cluster Survey (EDisCS) --- we analyze the galaxy stellar mass
distribution as a function of local density in mass-limited samples, in the
field and in clusters from low (z>0.04) to high (z<0.8) redshift. We find that
at all redshifts and in all environments, local density plays a role in shaping
the mass distribution. In the field, it regulates the shape of the mass
function at any mass above the mass limits. In clusters, it seems to be
important only at low masses (log M_ast/M_sun <10.1 in WINGS and log
M_ast/M_sun < 10.4 in EDisCS), otherwise it seems not to influence the mass
distribution. Putting together our results with those of Calvi et al. and
Vulcani et al. for the global environment, we argue that at least at local density is more important than global environment in determining the
galaxy stellar mass distribution, suggesting that galaxy properties are not
much dependent of halo mass, but do depend on local scale processes.Comment: MNRAS accepted, in pres
Fighting the Huntington's Disease with a G-Quadruplex-Forming Aptamer Specifically Binding to Mutant Huntingtin Protein: Biophysical Characterization, In Vitro and In Vivo Studies
A set of guanine-rich aptamers able to preferentially recognize full-length huntingtin with an expanded polyglutamine tract has been recently identified, showing high efficacy in modulating the functions of the mutated protein in a variety of cell experiments. We here report a detailed biophysical characterization of the best aptamer in the series, named MS3, proved to adopt a stable, parallel G-quadruplex structure and show high nuclease resistance in serum. Confocal microscopy experiments on HeLa and SH-SY5Y cells, as models of non-neuronal and neuronal cells, respectively, showed a rapid, dose-dependent uptake of fluorescein-labelled MS3, demonstrating its effective internalization, even in the absence of transfecting agents, with no general cytotoxicity. Then, using a well-established Drosophila melanogaster model for Huntington's disease, which expresses the mutated form of human huntingtin, a significant improvement in the motor neuronal function in flies fed with MS3 was observed, proving the in vivo efficacy of this aptamer
Truncated Analogues of a G-Quadruplex-Forming Aptamer Targeting Mutant Huntingtin: Shorter Is Better!
Two analogues of the MS3 aptamer, which was previously shown to have an exquisite capability to selectively bind and modulate the activity of mutant huntingtin (mHTT), have been here designed and evaluated in their physicochemical and biological properties. Featured by a distinctive propensity to form complex G-quadruplex structures, including large multimeric aggregates, the original 36-mer MS3 has been truncated to give a 33-mer (here named MS3-33) and a 17-mer (here named MS3-17). A combined use of different techniques (UV, CD, DSC, gel electrophoresis) allowed a detailed physicochemical characterization of these novel G-quadruplex-forming aptamers, tested in vitro on SH-SY5Y cells and in vivo on a Drosophila Huntington’s disease model, in which these shorter MS3-derived oligonucleotides proved to have improved bioactivity in comparison with the parent aptamer
The Padova-Millennium Galaxy and Group Catalogue (PM2GC): the group-finding method and the PM2GC catalogues of group, binary and single field galaxies
We present the construction and describe the properties of the
Padova-Millennium Galaxy and Group Catalogue (PM2GC), a galaxy catalogue
representative of the general field population in the local Universe. We
characterize galaxy environments by identifying galaxy groups at 0.04<=z<=0.1
with a Friends-of-Friends (FoF) algorithm using a complete sample of 3210
galaxies brighter than MB = -18.7 taken from the Millennium Galaxy Catalogue
(MGC, Liske et al. (2003)), a 38deg^2 photometric and spectroscopic equatorial
survey. We identified 176 groups with at least three members, comprising in
total 1057 galaxies and representing ~43 per cent of the general field
population in that redshift range. The median redshift and velocity dispersion
of our groups are 0.0823 and 192 km s^-1, respectively. 88 per cent of the
groups have fewer than ten members, and 63 per cent have fewer than five
members. Nongroup galaxies were subdivided into "inary" systems of two bright
close companions, and "single" galaxies with no companion, in order to identify
different environments useful for future scientific analysis. We performed a
detailed comparison with the 2PIGG catalogue to validate the effectiveness of
our method and the robustness of our results. Galaxy stellar masses are
computed for all PM2GC galaxies, and found to be in good agreement with Sloan
Digital Survey Data Release 7 (SDSS-DR7) mass estimates. The catalogues of
PM2GC groups, group properties and galaxy properties in all environments are
publicly available on theWorld Wide Web.Comment: 14 pages, 7 figures, 6 tables. MNRAS accepted, in press. Tables 2, 3,
4, 5, 6 early available or on request to autho
Massive stars exploding in a He-rich circumstellar medium. VI. Observations of two distant Type Ibn supernova candidates discovered by La Silla-QUEST
We present optical observations of the peculiar stripped-envelope supernovae
(SNe) LSQ12btw and LSQ13ccw discovered by the La Silla-QUEST survey. LSQ12btw
reaches an absolute peak magnitude of M(g) = -19.3 +- 0.2, and shows an
asymmetric light curve. Stringent prediscovery limits constrain its rise time
to maximum light to less than 4 days, with a slower post-peak luminosity
decline, similar to that experienced by the prototypical SN~Ibn 2006jc.
LSQ13ccw is somewhat different: while it also exhibits a very fast rise to
maximum, it reaches a fainter absolute peak magnitude (M(g) = -18.4 +- 0.2),
and experiences an extremely rapid post-peak decline similar to that observed
in the peculiar SN~Ib 2002bj. A stringent prediscovery limit and an early
marginal detection of LSQ13ccw allow us to determine the explosion time with an
uncertainty of 1 day. The spectra of LSQ12btw show the typical narrow He~I
emission lines characterising Type Ibn SNe, suggesting that the SN ejecta are
interacting with He-rich circumstellar material. The He I lines in the spectra
of LSQ13ccw exhibit weak narrow emissions superposed on broad components. An
unresolved Halpha line is also detected, suggesting a tentative Type Ibn/IIn
classification. As for other SNe~Ibn, we argue that LSQ12btw and LSQ13ccw
likely result from the explosions of Wolf-Rayet stars that experienced
instability phases prior to core collapse. We inspect the host galaxies of SNe
Ibn, and we show that all of them but one are hosted in spiral galaxies, likely
in environments spanning a wide metallicity range.Comment: 15 pages, 9 figures, 4 tables. Accepted by MNRA
- …