Is AGN feedback necessary to form red elliptical galaxies?

We have used GADGET2 to simulate the formation of an elliptical galaxy in a cosmological dark matter halo with mass 3x10^12M_Sun/h. Using a stellar population synthesis model has allowed us to compute magnitudes, colours and surface brightness profiles. We have included a model to follow the growth of a central black hole and we have compared the results of simulations with and without feedback from AGNs. We have studied the interplay between cold gas accretion and merging in the development of galactic morphologies, the link between colour and morphology evolution, the effect of AGN feedback on the photometry of early type galaxies, the redshift evolution in the properties of quasar hosts, and the impact of AGN winds on the chemical enrichment of the intergalactic medium (IGM). We have found that the early phases of galaxy formation are driven by the accretion of cold filamentary flows, which form a disc at the centre of the dark matter halo. When the dark matter halo is sufficiently massive to support the propagation of a stable shock, cold accretion is shut down, and the star formation rate begins to decline. Mergers transform the disc into an elliptical galaxy, but also bring gas into the galaxy. Without a mechanism that removes gas from the merger remnants, the galaxy ends up with blue colours, atypical for its elliptical morphology. AGN feedback can solve this problem even with a fairly low heating efficiency. We have also demonstrated that AGN winds are potentially important for the metal enrichment of the IGM a high redshift.(abridged)Comment: 19 pages and 17 figures, accepted to MNRAS ID: MN-07-1954-MJ.R1 . For high resolution images please check following link: http://www.aip.de/People/AKhalatyan/COSMOLOGY/BHCOSMO

Radiation hardness of CMS pixel barrel modules

Pixel detectors are used in the innermost part of the multi purpose experiments at LHC and are therefore exposed to the highest fluences of ionising radiation, which in this part of the detectors consists mainly of charged pions. The radiation hardness of all detector components has thoroughly been tested up to the fluences expected at the LHC. In case of an LHC upgrade, the fluence will be much higher and it is not yet clear how long the present pixel modules will stay operative in such a harsh environment. The aim of this study was to establish such a limit as a benchmark for other possible detector concepts considered for the upgrade. As the sensors and the readout chip are the parts most sensitive to radiation damage, samples consisting of a small pixel sensor bump-bonded to a CMS-readout chip (PSI46V2.1) have been irradiated with positive 200 MeV pions at PSI up to 6E14 Neq and with 21 GeV protons at CERN up to 5E15 Neq. After irradiation the response of the system to beta particles from a Sr-90 source was measured to characterise the charge collection efficiency of the sensor. Radiation induced changes in the readout chip were also measured. The results show that the present pixel modules can be expected to be still operational after a fluence of 2.8E15 Neq. Samples irradiated up to 5E15 Neq still see the beta particles. However, further tests are needed to confirm whether a stable operation with high particle detection efficiency is possible after such a high fluence.Comment: Contribution to the 11th European Symposium on Semiconductor Detectors June 7-11, 2009 Wildbad Kreuth, German

Parameters for > 300 million Gaia stars: Bayesian inference vs. machine learning

The Gaia Data Release 3 (DR3), published in June 2022, delivers a diverse set of astrometric, photometric, and spectroscopic measurements for more than a billion stars. The wealth and complexity of the data makes traditional approaches for estimating stellar parameters for the full Gaia dataset almost prohibitive. We have explored different supervised learning methods for extracting basic stellar parameters as well as distances and line-of-sight extinctions, given spectro-photo-astrometric data (including also the new Gaia XP spectra). For training we use an enhanced high-quality dataset compiled from Gaia DR3 and ground-based spectroscopic survey data covering the whole sky and all Galactic components. We show that even with a simple neural-network architecture or tree-based algorithm (and in the absence of Gaia XP spectra), we succeed in predicting competitive results (compared to Bayesian isochrone fitting) down to faint magnitudes. We will present a new Gaia DR3 stellar-parameter catalogue obtained using the currently best-performing machine-learning algorithm for tabular data, XGBoost, in the near future.Comment: To appear in Highlights of Spanish Astrophysics XI, Proceedings of the XV Scientific Meeting of the Spanish Astronomical Society held on September 4 - 9, 2022, in La Laguna, Spai

The Dependence of the Mass Assembly History of Cold Dark Matter Halos on Environment

We show by means of a high-resolution N-body simulation how the mass assembly histories of galaxy-size cold dark matter (CDM) halos depend on environment. Halos in high density environments form earlier and a higher fraction of their mass is assembled in major mergers,compared to low density environments. The distribution of the present--day specific mass aggregation rate is bimodal and strongly dependent on environment. While in low density environments only ~20% of the halos are not accreting mass at the present epoch, this fraction rises to ~80% at high densities. At z=1 the median of the specific aggregation rate is ~4 times larger than at z=0 and almost independent on environment. All the dependences on environment found here are critically enhanced by local processes associated to subhalos because the fraction of subhalos increases as the environment gets denser. The distribution of the halo specific mass aggregation rate as well as its dependence on environment resemble the relations for the specific star formation rate distribution of galaxies. An analogue of the morphology-density relation is also present at the level of CDM halos, being driven by the halo major merging history. Nevertheless, baryonic processes are necessary in order to explain further details and the evolution of the star formation rate-, color- and morphology-environment relations

Insights from super-metal-rich stars: Is the Milky Way bar young?

Context. Bar formation and merger events can contribute to the rearrangement of stars within the Galaxy in addition to triggering star formation (SF) epochs. Super-metal-rich (SMR) stars found in the solar neighbourhood (SNd) can be used as tracers of such events as they are expected to originate only in the inner Galaxy and to have definitely migrated. Aims. We study a homogeneous and large sample of SMR stars in the SNd to provide tighter constraints on the epoch of the bar formation and its impact on the Milky Way (MW) disc stellar populations. Methods. We investigated a sample of 169 701 main sequence turnoff (MSTO) and subgiant branch (SGB) stars with 6D phase space information and high-quality stellar parameters coming from the hybrid-CNN analysis of the Gaia-DR3 RVS stars. We computed distances and ages using the StarHorse code with a mean precision of 1% and 11%, respectively. Of these stars, 11 848 have metallicity ([Fe/H]) above 0.15 dex. Results. We report a metallicity dependence of spatial distribution of stellar orbits shown by the bimodal distribution in the guiding radius (Rg) at 6.9 and 7.9 kpc, first appearing at [Fe/H] ~ 0.1 dex, becoming very pronounced at higher [Fe/H]. In addition, we observe a trend where the most metal-rich stars, with [Fe/H] ~ 0.4 dex, are predominantly old (9–12 Gyr), but show a gradual decline in [Fe/H] with age, reaching approximately 0.25 dex about 4 Gyr ago, followed by a sharp drop around 3 Gyr ago. Furthermore, our full dataset reveals a clear peak in the age–metallicity relationship during the same period, indicating a SF burst around 3–4 Gyr ago with slightly sub-solar [Fe/H] and enhanced [α/Fe]. Conclusions. We show that the SMR stars are good tracers of bar activity.We interpret the steep decrease in the number of SMR stars at around 3 Gyr as the end of the bar formation epoch. In this scenario the peak of bar activity also coincides with a peak in the SF activity in the disc. Although the SF burst around 3 Gyr ago has been reported previously, its origin was unclear. Here we suggest that the SF burst was triggered by the high bar activity, 3–4 Gyr ago. According to these results and interpretation, the MW bar could be young

Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia DR2 stars brighter than G = 18

Combining the precise parallaxes and optical photometry delivered by Gaia's second data release (Gaia DR2) with the photometric catalogues of PanSTARRS-1, 2MASS, and AllWISE, we derive Bayesian stellar parameters, distances, and extinctions for 265 million stars brighter than G=18. Because of the wide wavelength range used, our results substantially improve the accuracy and precision of previous extinction and effective temperature estimates. After cleaning our results for both unreliable input and output data, we retain 137 million stars, for which we achieve a median precision of 5% in distance, 0.20 mag in V-band extinction, and 245 K in effective temperature for G<14, degrading towards fainter magnitudes (12%, 0.20 mag, and 245 K at G=16; 16%, 0.23 mag, and 260 K at G=17, respectively). We find a very good agreement with the asteroseismic surface gravities and distances of 7000 stars in the Kepler, the K2-C3, and the K2-C6 fields, with stellar parameters from the APOGEE survey, as well as with distances to star clusters. Our results are available through the ADQL query interface of the Gaia mirror at the Leibniz-Institut f\"{u}r Astrophysik Potsdam (gaia.aip.de) and as binary tables at data.aip.de. As a first application, in this paper we provide distance- and extinction-corrected colour-magnitude diagrams, extinction maps as a function of distance, and extensive density maps, demonstrating the potential of our value-added dataset for mapping the three-dimensional structure of our Galaxy. In particular, we see a clear manifestation of the Galactic bar in the stellar density distributions, an observation that can almost be considered a direct imaging of the Galactic bar.Comment: 25 pages, 23 figures + appendix, accepted for publication in A&A. Data (doi:10.17876/gaia/dr.2/51) are available through ADQL queries at gaia.aip.d

How strange are compact star interiors ?

We discuss a Nambu--Jona-Lasinio (NJL) type quantum field theoretical approach to the quark matter equation of state with color superconductivity and construct hybrid star models on this basis. It has recently been demonstrated that with increasing baryon density, the different quark flavors may occur sequentially, starting with down-quarks only, before the second light quark flavor and at highest densities also the strange quark flavor appears. We find that color superconducting phases are favorable over non-superconducting ones which entails consequences for thermodynamic and transport properties of hybrid star matter. In particular, for NJL-type models no strange quark matter phases can occur in compact star interiors due to mechanical instability against gravitational collapse, unless a sufficiently strong flavor mixing as provided by the Kobayashi-Maskawa-'t Hooft determinant interaction is present in the model. We discuss observational data on mass-radius relationships of compact stars which can put constraints on the properties of dense matter equation of state.Comment: 7 pages, 2 figures, to appear in the Proceedings of the International Conference SQM2009, Buzios, Rio de Janeiro, Brazil, Sep.27-Oct.2, 200

The A4 project: physics data processing using the Google protocol buffer library

In this paper, we present the High Energy Physics data format, processing toolset and analysis library a4, providing fast I/O of structured data using the Google protocol buffer library. The overall goal of a4 is to provide physicists with tools to work efficiently with billions of events, providing not only high speeds, but also automatic metadata handling, a set of UNIX-like tools to operate on a4 files, and powerful and fast histogramming capabilities. At present, a4 is an experimental project, but it has already been used by the authors in preparing physics publications. We give an overview of the individual modules of a4, provide examples of use, and supply a set of basic benchmarks. We compare a4 read performance with the common practice of storing unstructured data in ROOT trees. For the common case of storing a variable number of floating-point numbers per event, speedups in read speed of up to a factor of six are observed.Comment: Proceedings of poster shown at the 2012 International Conference on Computing in High Energy and Nuclear Physics (CHEP 2012). 19 pages, 17 figure

4MOST Consortium Survey 3: Milky Way Disc and Bulge Low-Resolution Survey (4MIDABLE-LR)

The mechanisms of the formation and evolution of the Milky Way are encoded in the orbits, chemistry and ages of its stars. With the 4MOST MIlky way Disk And BuLgE Low-Resolution Survey (4MIDABLE-LR) we aim to study kinematic and chemical substructures in the Milky Way disc and bulge region with samples of unprecedented size out to larger distances and greater precision than conceivable with Gaia alone or any other ongoing or planned survey. Gaia gives us the unique opportunity for target selection based almost entirely on parallax and magnitude range, hence increasing the efficiency in sampling larger Milky Way volumes with well-defined and effective selection functions. Our main goal is to provide a detailed chrono-chemo-kinematical extended map of our Galaxy and the largest Gaia follow-up down to $G = 19$ magnitudes (Vega). The complex nature of the disc components (for example, large target densities and highly structured extinction distribution in the Milky Way bulge and disc area), prompted us to develop a survey strategy with five main sub-surveys that are tailored to answer the still open questions about the assembly and evolution of our Galaxy, while taking full advantage of the Gaia data.Comment: Part of the 4MOST issue of The Messenger, published in preparation of 4MOST Community Workshop, see http://www.eso.org/sci/meetings/2019/4MOST.htm