11 research outputs found
Disk galaxies with broken luminosity profiles from cosmological simulations
We present SPH cosmological simulations of the formation of three disk
galaxies with a detailed treatment of chemical evolution and cooling. The
resulting galaxies have properties compatible with observations: relatively
high disk-to-total ratios, thin stellar disks and good agreement with the
Tully-Fisher and the luminosity-size relations. They present a break in the
luminosity profile at 3.0 +- 0.5 disk scale lengths, while showing an
exponential mass profile without any apparent breaks, in line with recent
observational results. Since the stellar mass profile is exponential, only
differences in the stellar populations can be the cause of the luminosity
break. Although we find a cutoff for the star formation rate imposed by a
density threshold in our star formation model, it does not coincide with the
luminosity break and is located at 4.3 +- 0.4 disk scale lengths, with star
formation going on between both radii. The color profiles and the age profiles
are "U-shaped", with the minimum for both profiles located approximately at the
break radius. The SFR to stellar mass ratio increases until the break,
explaining the coincidence of the break with the minimum of the age profile.
Beyond the break we find a steep decline in the gas density and, consequently,
a decline in the SFR and redder colors. We show that most stars (64-78%) in the
outer disk originate in the inner disk and afterwards migrate there. Such
stellar migrations are likely the main origin of the U-shaped age profile and,
therefore, of the luminosity break.Comment: 8 pages, 4 figures. Accepted by ApJ
A two-phase scenario for bulge assembly in ΛcDM cosmologies
The Astrophysical Journal 763.1 (2013): 26 reproduced by permission of the AASWe analyze and compare the bulges of a sample of L* spiral galaxies in hydrodynamical simulations in a cosmological context, using two different codes, P-DEVA and GASOLINE. The codes regulate star formation in very different ways, with P-DEVA simulations inputting low star formation efficiency under the assumption that feedback occurs on subgrid scales, while the GASOLINE simulations have feedback that drives large-scale outflows. In all cases, the marked knee shape in mass aggregation tracks, corresponding to the transition from an early phase of rapid mass assembly to a later slower one, separates the properties of two populations within the simulated bulges. The bulges analyzed show an important early starburst resulting from the collapse-like fast phase of mass assembly, followed by a second phase with lower star formation, driven by a variety of processes such as disk instabilities and/or mergers. Classifying bulge stellar particles identified at z = 0 into old and young according to these two phases, we found bulge stellar sub-populations with distinct kinematics, shapes, stellar ages, and metal contents. The young components are more oblate, generally smaller, more rotationally supported, with higher metallicity and less alpha-element enhanced than the old ones. These results are consistent with the current observational status of bulges, and provide an explanation for some apparently paradoxical observations, such as bulge rejuvenation and metal-content gradients observed. Our results suggest that bulges of L* galaxies will generically have two bulge populations that can be likened to classical and pseudo-bulges, with differences being in the relative proportions of the two, which may vary due to galaxy mass and specific mass accretion and merger histories.This work was partially supported by the MICINN (Spain) through the grants AYA2009-12792-C03-02 and AYA2009-12792-C03-03 from the PNAyA, as well as by the regional Madrid V PRICIT program through the ASTROMADRID network (CAM S2009/ESP-1496) and the “Supercomputación y e-Ciencia” Consolider-Ingenio CSD2007-0050 project
Thin disc, Thick Disc and Halo in a Simulated Galaxy
Within a cosmological hydrodynamical simulation, we form a disc galaxy with
sub- components which can be assigned to a thin stellar disc, thick disk, and a
low mass stellar halo via a chemical decomposition. The thin and thick disc
populations so selected are distinct in their ages, kinematics, and
metallicities. Thin disc stars are young (<6.6 Gyr), possess low velocity
dispersion ({\sigma}U,V,W = 41, 31, 25 km/s), high [Fe/H], and low [O/Fe]. The
thick disc stars are old (6.6<age<9.8 Gyrs), lag the thin disc by \sim21 km/s,
possess higher velocity dispersion ({\sigma}U,V,W = 49, 44, 35 km/s),
relatively low [Fe/H] and high [O/Fe]. The halo component comprises less than
4% of stars in the "solar annulus" of the simulation, has low metallicity, a
velocity ellipsoid defined by ({\sigma}U,V,W = 62, 46, 45 km/s) and is formed
primarily in-situ during an early merger epoch. Gas-rich mergers during this
epoch play a major role in fuelling the formation of the old disc stars (the
thick disc). This is consistent with studies which show that cold accretion is
the main source of a disc galaxy's baryons. Our simulation initially forms a
relatively short (scalelength \sim1.7 kpc at z=1) and kinematically hot disc,
primarily from gas accreted during the galaxy's merger epoch. Far from being a
competing formation scenario, migration is crucial for reconciling the short,
hot, discs which form at high redshift in {\Lambda}CDM, with the properties of
the thick disc at z=0. The thick disc, as defined by its abundances maintains
its relatively short scale-length at z = 0 (2.31 kpc) compared with the total
disc scale-length of 2.73 kpc. The inside-out nature of disc growth is
imprinted the evolution of abundances such that the metal poor {\alpha}-young
population has a larger scale-length (4.07 kpc) than the more chemically
evolved metal rich {\alpha}-young population (2.74 kpc).Comment: Submitted to MNRAS. This version after helpful referee comments.
Comments welcome to [email protected]
Formation of galaxies in {\Lambda}CDM cosmologies. I. The fine structure of disc galaxies
We present a detailed analysis of the global and fine structure of four
middle-mass disc galaxies obtained from simulations in a CDM scenario.
These objects have photometric D/T ratios in good agreement with those observed
for late-type spirals, as well as kinematic properties in agreement with the
observational Tully-Fisher relation. We identify the different dynamical
components at z=0 on the basis of both orbital parameters and the binding
energy of stars in the galaxy. In this way, we recognize a slowly rotating
centrally concentrated spheroid, and two disc components supported by rotation:
a thin disc with stars in nearly circular orbits, and a thick disc with orbital
parameters transitional between the thin disc and the spheroid. The spheroidal
component is composed mainly by old, metal-poor and {\alpha}-enhanced stars.
The distribution of metals in this component shows, however, a clear bimodality
with a low-metallicity peak, which could be related to a classical bulge, and a
high-metallicity peak, which could be related to a pseudo-bulge. The thin disc
appears in our simulations as the youngest and most metal-rich component. The
radial distribution of ages and colours in this component are U-shaped: the new
stars are forming in the inner regions, and then migrate through secular
processes. Finally, we also find a thick disc containing about 16% of the total
stellar mass and with properties that are intermediate between those of the
thin disc and the spheroid. Its low-metallicity stars are {\alpha}-enhanced
when compared to thin disc stars of the same metallicity. The structural
parameters (e.g., the scale height) of the simulated thick discs suggest that
such a component could result from the combination of different thickening
mechanisms that include merger-driven processes, but also long-lived internal
perturbations of the thin disc. [Abridged]Comment: 23 pages, 16 figures, accepted for publication in MNRAS, references
fixe
Monoclonal antibodies to a high molecular weight isoform of porcine CD45 Biochemical and tissue distribution analyses
This report describes the obtention and characterization of two monoclonal antibodies (mAbs), 6E3/7 [mAb 6E3/7 was submitted to the Second International Swine CD Workshop, where it has been assigned to CD45R] and 3C3/9, which recognize the isoform of highest molecular weight of porcine CD45. This conclusion is based on their cell reactivity anti tissue distribution, identical to that reported for the human high molecular weight isoform of CD45, and on data from immunoprecipitation anti immunoblotting analyses which show that these mAbs react with the largest polypeptide of those precipitated by mAb 2A5, that recognizes an epitope shared by all CD45 isoforms. These mAbs react with 60% of peripheral blood mononuclear cells (PBMC) but not with alveolar macrophages, granulocytes, platelets or erythrocytes. Antigen expression on PBMC is heterogeneous and is reduced after in vitro activation with mitogens. B cells and CD8+ T cells express more antigen than CD4+ T cells. Using immunoperoxidase techniques, the antigen was detected on B cell areas of lymph nodes and Peyer's patches, and on a subpopulation of medullary thymocytes. These mAbs will be useful reagents for functional and phenotypic analysis of porcine lymphoid cell populations by flow cytometry and immunohistochemistry
Monoclonal antibodies 2F6/8 and 2A10/8 recognize a porcine antigen (SWC7) expressed on B cells and activated T cells
This report describes the production and characterization of two monoclonal antibodies (mAbs), 2F6/8 and 2A10/8, that recognize a porcine antigen (SWC7) expressed on B cells in lymphoid tissues. The antigen was not detectable on resting PBMC but its expression could be induced after treatment with phorbol esters (PMA) but not by ConA, PWM, LPS or Ca ionophore. Kinetic studies showed that the antigen was expressed 24 h after PMA treatment, peaked at day 2 or 3 and slightly declined by day 6. Interestingly, the antigen was also found on a subset of CD3 + T cells, with levels of expression similar to those of B cells. By immunohistochemistry, the antigen was detected on follicular dendritic cells of germinal centers in tonsils, spleen, lymph nodes and Peyer's patches. MAb 2F6/8 precipitates a molecule of approximately 40 kDa under non-reducing conditions, and 24 kDa under reducing conditions. The restricted and tightly regulated expression of this antigen may reflect an important role in B cell differentiation within the germinal center. These mAbs will be useful reagents for phenotypic analysis of porcine lymphoid cell populations by flow cytometry and immunohistochemistry
Molecular and functional characterization of porcine LFA-1 using monoclonal antibodies to CD11a and CD18
We describe in this report the production and characterization of monoclonal antibodies (mAb) to the swine homologues of CD11a and CD18 antigens, and their use for phenotypic and functional analysis of porcine leukocytes. Monoclonal antibodies BL1H8 and BL2F1 precipitated two bands of approximately 170 and 95 kDa, whereas mAb BA3H2 brought down three bands of 170, 155 and 95 kDa, from alveolar macrophage lysates. Clearance of macrophage lysates with mAbs BL1H8 and BL2F1 resulted in complete removal of the 170-kDa band. The cell distribution of the molecules recognized by these mAbs was similar to that of human LFA-1. It was found on all leukocytes, although its expression varied among the different leukocyte subpopulations, with monocytes, granulocytes and a subset of CD8+ cells expressing the highest levels. Cross-blocking studies showed that these antibodies recognize different epitopes on porcine LFA-1. Both anti-LFA-1 mAbs strongly inhibited the mitogenic response of PBMC to ConA, whereas the anti-CD18 mAb had no effect. These anti-LFA-1 mAbs also inhibited the mixed lymphocyte reaction (MLR) and the NK cell-mediated lysis of K-562 cells