153 research outputs found
Lights in the Dark: Globular clusters as dark matter tracers
A long-standing observed curiosity of globular clusters (GCs) has been that
both the number and total mass of GCs in a galaxy are linearly correlated with
the galaxy's virial mass, whereas its stellar component shows no such linear
correlation. This work expands on an empirical model for the numbers and ages
of GCs in galaxies presented by Valenzuela et al. (2021) that is consistent
with recent observational data from massive elliptical galaxies down to the
dwarf galaxy regime. Applying the model to simulations, GC numbers are shown to
be excellent tracers for the dark matter (DM) virial mass, even when distinct
formation mechanisms are employed for blue and red GCs. Furthermore, the amount
of DM smooth accretion is encoded in the GC abundances, therefore providing a
measure for an otherwise nearly untraceable component of the formation history
of galaxies.Comment: 5 pages, 3 figures, to be published in Memorie della SAI
On the Sensitivity of Halo Shape Measurements
Shape measurements of galaxies and galaxy clusters are widespread in the
analysis of cosmological simulations. But the limitations of those measurements
have been poorly investigated. In this paper, we explain why the quality of the
shape measurement does not only depend on the numerical resolution, but also on
the density gradient. In particular, this can limit the quality of measurements
in the central regions of haloes. We propose a criterion to estimate the
sensitivity of the measured shapes based on the density gradient of the halo
and apply it to cosmological simulations of collisionless and self-interacting
dark matter. By this, we demonstrate where reliable measurements of the halo
shape are possible and how cored density profiles limit their applicability.Comment: 5 pages, 2 figures + appendices, submitted to A&
Revised Simulations of the Planetary Nebulae Luminosity Function
We describe a revised procedure for the numerical simulation of planetary nebulae luminosity functions (PNLFs), improving on previous work. The procedure is now based on new H-burning post-asymptotic giant branch (AGB) evolutionary tracks. For a given stellar mass, the new central stars are more luminous and evolve faster. We have slightly changed the distribution of the [O iii] 5007 intensities relative to those of HÎČ and the generation of absorbing factors, while still basing their numerical modeling on empirical information extracted from studies of galactic planetary nebulae (PNs) and their central stars. We argue that the assumption of PNs being completely optically thick to H-ionizing photons leads to conflicts with observations and show that to account for optically thin PNs is necessary. We then use the new simulations to estimate a maximum final mass, clarifying its meaning, and discuss the effect of internal dust extinction as a possible way of explaining the persistent discrepancy between PNLFs and surface brightness fluctuation distances. By adjusting the range of minimum to maximum final mass, it is also possible to explain the observed variety of PNLF shapes at intermediate magnitudes. The new PN formation rates are calculated to be slightly lower than suggested by previous simulations based on older post-AGB evolutionary tracks.Fil: Valenzuela, Lucas M.. Ludwig Maximilians Universitat; AlemaniaFil: MĂ©ndez, Roberto. University of Hawaii at Manoa; Estados UnidosFil: Miller Bertolami, Marcelo Miguel. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto de AstrofĂsica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias AstronĂłmicas y GeofĂsicas. Instituto de AstrofĂsica La Plata; Argentin
Blowing out the Candle: How to Quench Galaxies at High Redshift -- an Ensemble of Rapid Starbursts, AGN Feedback and Environment
Recent observations with JWST and ALMA have revealed extremely massive
quiescent galaxies at redshifts of z=3 and higher, indicating both rapid onset
and quenching of star formation. Using the cosmological simulation suite
Magneticum Pathfinder we reproduce the observed number densities and stellar
masses, with 36 quenched galaxies of stellar mass larger than 3e10Msun at
z=3.42. We find that these galaxies are quenched through a rapid burst of
star-formation and subsequent AGN feedback caused by a particularly isotropic
collapse of surrounding gas, occurring on timescales of around 200Myr or
shorter. The resulting quenched galaxies host stellar components which are
kinematically fast rotating and alpha-enhanced, while exhibiting a steeper
metallicity and flatter age gradient compared to galaxies of similar stellar
mass. The gas of the galaxies has been metal enriched and ejected. We find that
quenched galaxies do not inhabit the densest nodes, but rather sit in local
underdensities. We analyze observable metrics to predict future quenching at
high redshifts, finding that on shorter timescales <500Myr the ratio M_bh/M_*
is the best predictor, followed by the burstiness of the preceding
star-formation, t50-t90 (time to go from 50% to 90% stellar mass). On longer
timescales, >1Gyr, the environment becomes the strongest predictor, followed by
t50-t90, indicating that at high redshifts the consumption of old and lack of
new gas are more relevant for long-term prevention of star-formation than the
presence of a massive AGN. We predict that relics of such high-z quenched
galaxies should best be characterized by a strong alpha enhancement.Comment: 22 pages, 13 figures, Submitted to ApJ, Comments welcom
Globular cluster numbers in dark matter haloes in a dual formation scenario: an empirical model within EMERGE
We present an empirical model for the number of globular clusters (GCs) in
galaxies based on recent data showing a tight relationship between dark matter
halo virial masses and GC numbers. While a simple base model forming GCs in
low-mass haloes reproduces this relation, we show that a second formation
pathway for GCs is needed to account for observed younger GC populations. We
confirm previous works that reported the observed linear correlation as being a
consequence of hierarchical merging and its insensitivity to the exact GC
formation processes at higher virial masses, even for a dual formation
scenario. We find that the scatter of the linear relation is strongly
correlated with the relative amount of smooth accretion: the more dark matter
is smoothly accreted, the fewer GCs a halo has compared to other haloes of the
same mass. This scatter is smaller than that introduced by halo mass
measurements, indicating that the number of GCs in a galaxy is a good tracer
for its dark matter mass. Smooth accretion is also the reason for a lower
average dark matter mass per GC in low-mass haloes. Finally, we successfully
reproduce the observed general trend of GCs being old and the tendency of more
massive haloes hosting older GC systems. Including the second GC formation
mechanism through gas-rich mergers leads to a more realistic variety of GC age
distributions and also introduces an age inversion in the halo virial mass
range .Comment: 18 pages, 19 figures, accepted for publication in MNRA
The MAGPI Survey: Effects of Spiral Arms on Different Tracers of the Interstellar Medium and Stellar Populations at z~0.3
Spiral structures are important drivers of the secular evolution of disc
galaxies, however, the origin of spiral arms and their effects on the
development of galaxies remain mysterious. In this work, we present two
three-armed spiral galaxies at z~0.3 in the Middle Age Galaxy Properties with
Integral Field Spectroscopy (MAGPI) survey. Taking advantage of the high
spatial resolution (~0.6'') of the Multi-Unit Spectroscopic Unit (MUSE), we
investigate the two-dimensional distributions of different spectral parameters:
Halpha, gas-phase metallicity, and D4000. We notice significant offsets in
Halpha (~0.2 dex) as well as gas-phase metallicities (~0.05 dex) among the
spiral arms, downstream and upstream of MAGPI1202197197 (SG1202). This
observational signature suggests the spiral structure in SG1202 is consistent
with arising from density wave theory. No azimuthal variation in Halpha or
gas-phase metallicities is observed in MAGPI1204198199 (SG1204), which can be
attributed to the tighter spiral arms in SG1204 than SG1202, coming with
stronger mixing effects in the disc. The absence of azimuthal D4000 variation
in both galaxies suggests the stars at different ages are well-mixed between
the spiral arms and distributed around the disc regions. The different
azimuthal distributions in Halpha and D4000 highlight the importance of time
scales traced by various spectral parameters when studying 2D distributions in
spiral galaxies. This work demonstrates the feasibility of constraining spiral
structures by tracing interstellar medium (ISM) and stellar population at
z~0.3, with a plan to expand the study to the full MAGPI survey.Comment: 15 pages, 11 figures, 2 tables, accepted for publication in MNRA
The MAGPI Survey: impact of environment on the total internal mass distribution of galaxies in the last 5 Gyr
We investigate the impact of environment on the internal mass distribution of galaxies using the Middle Ages Galaxy Properties with Integral field spectroscopy (MAGPI) survey. We use 2D resolved stellar kinematics to construct Jeans dynamical models for galaxies at mean redshift z ⌠0.3, corresponding to a lookback time of 3â4 Gyr. The internal mass distribution for each galaxy is parametrized by the combined mass density slope Îł (baryons + dark matter), which is the logarithmic change of density with radius. We use a MAGPI sample of 28 galaxies from low-to-mid density environments and compare to density slopes derived from galaxies in the high density Frontier Fields clusters in the redshift range 0.29 < z < 0.55, corresponding to a lookback time of âŒ5 Gyr. We find a median density slope of Îł = â2.22 ± 0.05 for the MAGPI sample, which is significantly steeper than the Frontier Fields median slope (Îł = â2.00 ± 0.04), implying the cluster galaxies are less centrally concentrated in their mass distribution than MAGPI galaxies. We also compare to the distribution of density slopes from galaxies in ATLAS3D at z ⌠0, because the sample probes a similar environmental range as MAGPI. The ATLAS3D median total slope is Îł = â2.25 ± 0.02, consistent with the MAGPI median. Our results indicate environment plays a role in the internal mass distribution of galaxies, with no evolution of the slope in the last 3â4 Gyr. These results are in agreement with the predictions of cosmological simulations
Preferential Localization of Human Origins of DNA Replication at the 5âČ-Ends of Expressed Genes and at Evolutionarily Conserved DNA Sequences
Replication of mammalian genomes requires the activation of thousands of
origins which are both spatially and temporally regulated by as yet unknown
mechanisms. At the most fundamental level, our knowledge about the
distribution pattern of origins in each of the chromosomes, among different
cell types, and whether the physiological state of the cells alters this
distribution is at present very limited.We have used standard λ-exonuclease resistant nascent DNA preparations in
the size range of 0.7â1.5 kb obtained from the breast cancer cell line
MCFâ7 hybridized to a custom tiling array containing 50â60 nt
probes evenly distributed among genic and non-genic regions covering about
1% of the human genome. A similar DNA preparation was used for
high-throughput DNA sequencing. Array experiments were also performed with
DNA obtained from BT-474 and H520 cell lines. By determining the sites
showing nascent DNA enrichment, we have localized several thousand origins
of DNA replication. Our major findings are: (a) both array and DNA
sequencing assay methods produced essentially the same origin distribution
profile; (b) origin distribution is largely conserved (>70%) in
all cell lines tested; (c) origins are enriched at the 5âČends of
expressed genes and at evolutionarily conserved intergenic sequences; and
(d) ChIP on chip experiments in MCF-7 showed an enrichment of H3K4Me3 and
RNA Polymerase II chromatin binding sites at origins of DNA replication.Our results suggest that the program for origin activation is largely
conserved among different cell types. Also, our work supports recent studies
connecting transcription initiation with replication, and in addition
suggests that evolutionarily conserved intergenic sequences have the
potential to participate in origin selection. Overall, our observations
suggest that replication origin selection is a stochastic process
significantly dependent upon local accessibility to replication factors
Evolution in the orbital structure of quiescent galaxies from MAGPI, LEGA-C, and SAMI surveys: direct evidence for merger-driven growth over the last 7 Gyr
We present the first study of spatially integrated higher-order stellar kinematics over cosmic time. We use deep rest-frame optical spectroscopy of quiescent galaxies at redshifts z = 0.05, 0.3, and 0.8 from the SAMI, MAGPI, and LEGA-C surveys to measure the excess kurtosis h4 of the stellar velocity distribution, the latter parametrized as a Gauss-Hermite series. Conservatively using a redshift-independent cut in stellar mass (â â ) and matching the stellar-mass distributions of our samples, we find 7Ï evidence of h4 increasing with cosmic time, from a median value of 0.019 ± 0.002 at z = 0.8 to 0.059 ± 0.004 at z = 0.06. Alternatively, we use a physically motivated sample selection based on the mass distribution of the progenitors of local quiescent galaxies as inferred from numerical simulations; in this case, we find 10Ï evidence. This evolution suggests that, over the last 7 Gyr, there has been a gradual decrease in the rotation-to-dispersion ratio and an increase in the radial anisotropy of the stellar velocity distribution, qualitatively consistent with accretion of gas-poor satellites. These findings demonstrate that massive galaxies continue to accrete mass and increase their dispersion support after becoming quiescent
Different higher order kinematics between star-forming and quiescent galaxies based on the SAMI, MAGPI, and LEGA-C surveys
We present the first statistical study of spatially integrated non-Gaussian stellar kinematics spanning 7 Gyr in cosmic time. We use deep, rest-frame optical spectroscopy of massive galaxies (stellar mass â ) at redshifts z = 0.05, 0.3, and 0.8 from the SAMI, MAGPI, and LEGA-C surveys, to measure the excess kurtosis h4 of the stellar velocity distribution, the latter parametrized as a GaussâHermite series. We find that at all redshifts where we have large enough samples, h4 anticorrelates with the ratio between rotation and dispersion, highlighting the physical connection between these two kinematic observables. In addition, and independently from the anticorrelation with rotation-to-dispersion ratio, we also find a correlation between h4 and Mâ, potentially connected to the assembly history of galaxies. In contrast, after controlling for mass, we find no evidence of independent correlation between h4 and aperture velocity dispersion or galaxy size. These results hold for both star-forming and quiescent galaxies. For quiescent galaxies, h4 also correlates with projected shape, even after controlling for the rotation-to-dispersion ratio. At any given redshift, star-forming galaxies have lower h4 compared to quiescent galaxies, highlighting the link between kinematic structure and star-forming activity
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