The Overlooked Potential of Generalized Linear Models in Astronomy-III: Bayesian Negative Binomial Regression and Globular Cluster Populations

In this paper, the third in a series illustrating the power of generalized linear models (GLMs) for the astronomical community, we elucidate the potential of the class of GLMs which handles count data. The size of a galaxy's globular cluster population $N_{\rm GC}$ is a prolonged puzzle in the astronomical literature. It falls in the category of count data analysis, yet it is usually modelled as if it were a continuous response variable. We have developed a Bayesian negative binomial regression model to study the connection between $N_{\rm GC}$ and the following galaxy properties: central black hole mass, dynamical bulge mass, bulge velocity dispersion, and absolute visual magnitude. The methodology introduced herein naturally accounts for heteroscedasticity, intrinsic scatter, errors in measurements in both axes (either discrete or continuous), and allows modelling the population of globular clusters on their natural scale as a non-negative integer variable. Prediction intervals of 99% around the trend for expected $N_{\rm GC}$comfortably envelope the data, notably including the Milky Way, which has hitherto been considered a problematic outlier. Finally, we demonstrate how random intercept models can incorporate information of each particular galaxy morphological type. Bayesian variable selection methodology allows for automatically identifying galaxy types with different productions of GCs, suggesting that on average S0 galaxies have a GC population 35% smaller than other types with similar brightness.Comment: 14 pages, 12 figures. Accepted for publication in MNRA

The Hot Interstellar Medium in Normal Elliptical Galaxies III: The Thermal Structure of the Gas

This is the third paper in a series analyzing X-ray emission from the hot interstellar medium in a sample of 54 normal elliptical galaxies observed by Chandra, focusing on 36 galaxies with sufficient signal to compute radial temperature profiles. We distinguish four qualitatively different types of profile: positive gradient (outwardly rising), negative gradients (falling), quasi-isothermal (flat) and hybrid (falling at small radii, then rising). We measure the mean logarithmic temperature gradients in two radial regions: from 0--2 $J$-band effective radii $R_J$ (excluding the central point source), and from 2--$4R_J$. We find the outer gradient to be uncorrelated with intrinsic host galaxy properties, but strongly influenced by the environment: galaxies in low-density environments tend to show negative outer gradients, while those in high-density environments show positive outer gradients, suggesting influence of circumgalactic hot gas. The inner temperature gradient is unaffected by the environment but strongly correlated with intrinsic host galaxy characteristics: negative inner gradients are more common for smaller, optically faint, low radio-luminosity galaxies, whereas positive gradients are found in bright galaxies with stronger radio sources. There is no evidence for bimodality in the distribution of inner or outer gradients. We propose three scenarios to explain the inner temperature gradients: (1) Weak AGN heat the ISM locally, higher-luminosity AGN heat the system globally through jets inflating cavities at larger radii; (2) The onset of negative inner gradients indicates a declining importance of AGN heating relative to other sources, such as compressional heating or supernovae; (3) The variety of temperature profiles are snapshots of different stages of a time-dependent flow.Comment: 18 pages, emulateapj, 55 figures (36 online-only figures included in astro-ph version), submitted to Ap

Molecular gas and nuclear activity in early-type galaxies: any link with radio-loudness?

Aims. We want to study the amount of molecular gas in a sample of nearby early-type galaxies (ETGs) which host low-luminosity Active Galactic Nuclei (AGN). We look for possible differences between the radio-loud (RL) and radio-quiet (RQ) AGN. Methods. We observed the CO(1-0) and CO(2-1) spectral lines with the IRAM 30m and NRO 45m telescopes for eight galaxies. They belong to a large sample of 37 local ETGs which host both RQ and RL AGN. We gather data from the literature for the entire sample. Results. We report the new detection of CO(1-0) emission in four galaxies (UGC0968, UGC5617, UGC6946, and UGC8355) and CO(2-1) emission in two of them (UGC0968 and UGC5617). The CO(2-1)/CO(1-0) ratio in these sources is $\sim0.7\pm0.2$. Considering both the new observations and the literature, the detection rate of CO in our sample is 55 $\pm$ 9%, with no statistically significant difference between the hosts of RL and RQ AGNs. For all the detected galaxies we converted the CO luminosities into the molecular masses, $M_{H_2}$, that range from 10$^{6.5}$ to 10$^{8.5}$ M$_{\odot}$, without any statistically significant differences between RL and RQ galaxies. This suggests that the amount of molecular gas does not likely set the radio-loudness of the AGN. Furthermore, despite the low statistical significance, the presence of a weak trend between the H$_{2}$ mass with various tracers of nuclear activity (mainly [O III] emission line nuclear power) cannot be excluded.Comment: Accepted for publication on A&A, 9 pages, 5 figure

The zCOSMOS Redshift Survey: the role of environment and stellar mass in shaping the rise of the morphology-density relation from z~1

For more than two decades we have known that galaxy morphological segregation is present in the Local Universe. It is important to see how this relation evolves with cosmic time. To investigate how galaxy assembly took place with cosmic time, we explore the evolution of the morphology-density relation up to redshift z~1 using about 10000 galaxies drawn from the zCOSMOS Galaxy Redshift Survey. Taking advantage of accurate HST/ACS morphologies from the COSMOS survey, of the well-characterised zCOSMOS 3D environment, and of a large sample of galaxies with spectroscopic redshift, we want to study here the evolution of the morphology-density relation up to z~1 and its dependence on galaxy luminosity and stellar mass. The multi-wavelength coverage of the field also allows a first study of the galaxy morphological segregation dependence on colour. We further attempt to disentangle between processes that occurred early in the history of the Universe or late in the life of galaxies. The zCOSMOS field benefits of high-resolution imaging in the F814W filter from the Advanced Camera for Survey (ACS). We use standard morphology classifiers, optimised for being robust against band-shifting and surface brightness dimming, and a new, objective, and automated method to convert morphological parameters into early, spiral, and irregular types. We use about 10000 galaxies down to I_AB=22.5 with a spectroscopic sampling rate of 33% to characterise the environment of galaxies up to z~1 from the 100 kpc scales of galaxy groups up to the 100 Mpc scales of the cosmic web. ABRIDGEDComment: 23 pages, 12 figures, accepted for publication in Astronomy and Astrophysic

The instantaneous radial growth rate of stellar discs

We present a new and simple method to measure the instantaneous mass and radial growth rates of the stellar discs of spiral galaxies, based on their star formation rate surface density (SFRD) profiles. Under the hypothesis that discs are exponential with time-varying scalelengths, we derive a universal theoretical profile for the SFRD, with a linear dependence on two parameters: the specific mass growth rate $\nu_\textrm{M} \equiv \dot{M_\star}/M_\star$ and the specific radial growth rate $\nu_\textrm{R} \equiv \dot{R}_\star/R_\star$ of the disc. We test our theory on a sample of 35 nearby spiral galaxies, for which we derive a measurement of $\nu_\textrm{M}$ and $\nu_\textrm{R}$. 32/35 galaxies show the signature of ongoing inside-out growth ($\nu_\textrm{R} > 0$). The typical derived e-folding timescales for mass and radial growth in our sample are ~ 10 Gyr and ~ 30 Gyr, respectively, with some systematic uncertainties. More massive discs have a larger scatter in $\nu_\textrm{M}$ and $\nu_\textrm{R}$, biased towards a slower growth, both in mass and size. We find a linear relation between the two growth rates, indicating that our galaxy discs grow in size at ~ 0.35 times the rate at which they grow in mass; this ratio is largely unaffected by systematics. Our results are in very good agreement with theoretical expectations if known scaling relations of disc galaxies are not evolving with time.Comment: MNRAS, accepted. 14 pages, 4 figures, 3 tables. Additional material (Atlas.pdf) available at http://www.filippofraternali.com/downloads/index.htm

On the Link Between Central Black Holes, Bar Dynamics, and Dark Matter Halos in Spiral Galaxies

The discovery of a relationship between supermassive black hole (SMBH) mass and spiral arm pitch angle (P) is evidence that SMBHs are tied to the overall secular evolution of a galaxy. The discovery of SMBHs in late-type galaxies with little or no bulge suggests that an underlying correlation between the dark matter halo concentration and SMBH mass (MBH) exists, rather than between the bulge mass and MBH. In this paper we measure P using a two-dimensional fast fourier transform and estimate the bar pattern speeds of 40 barred spiral galaxies from the Carnegie-Irvine Galaxy Survey. The pattern speeds were derived by estimating the gravitational potentials of our galaxies from Ks-band images and using them to produce dynamical simulation models. The pattern speeds allow us to identify those galaxies with low central dark halo densities, or fast rotating bars, while P provides an estimate of MBH. We find that a wide range of MBH exists in galaxies with low central dark matter halo densities, which appears to support other theoretical results. We also find that galaxies with low central dark halo densities appear to follow more predictable trends in P versus de Vaucouleurs morphological type (T) and bar strength versus T than barred galaxies in general. The empirical relationship between MBH and total gravitational mass of a galaxy (Mtot) allows us to predict the minimum Mtot that will be observationally measured of our fast bar galaxies. These predictions will be investigated in a subsequent paper.Comment: 17 pages, 1 table, 11 figures, accepted for publication in MNRA

Euler Number and Percolation Threshold on a Square Lattice with Diagonal Connection Probability and Revisiting the Island-Mainland Transition

We report some novel properties of a square lattice filled with white sites, randomly occupied by black sites (with probability $p$). We consider connections up to second nearest neighbours, according to the following rule. Edge-sharing sites, i.e. nearest neighbours of similar type are always considered to belong to the same cluster. A pair of black corner-sharing sites, i.e. second nearest neighbours may form a 'cross-connection' with a pair of white corner-sharing sites. In this case assigning connected status to both pairs simultaneously, makes the system quasi-three dimensional, with intertwined black and white clusters. The two-dimensional character of the system is preserved by considering the black diagonal pair to be connected with a probability $q$, in which case the crossing white pair of sites are deemed disjoint. If the black pair is disjoint, the white pair is considered connected. In this scenario we investigate (i) the variation of the Euler number $\chi(p) \ [=N_B(p)-N_W(p)]$ versus $p$ graph for varying $q$, (ii) variation of the site percolation threshold with $q$ and (iii) size distribution of the black clusters for varying $p$, when $q=0.5$. Here $N_B$ is the number of black clusters and $N_W$ is the number of white clusters, at a certain probability $p$. We also discuss the earlier proposed 'Island-Mainland' transition (Khatun, T., Dutta, T. & Tarafdar, S. Eur. Phys. J. B (2017) 90: 213) and show mathematically that the proposed transition is not, in fact, a critical phase transition and does not survive finite size scaling. It is also explained mathematically why clusters of size 1 are always the most numerous

Knots in the outer shells of the planetary nebulae IC 2553 and NGC 5882

We present images and high-resolution spectra of the planetary nebulae IC 2553 and NGC 5882. Spatio-kinematic modeling of the nebulae shows that they are composed of a markedly elongated inner shell, and of a less aspherical outer shell expanding at a considerably higher velocity than the inner one. Embedded in the outer shells of both nebulae are found several low-ionization knots. In IC 2553, the knots show a point-symmetric distribution with respect to the central star: one possible explanation for their formation is that they are the survivors of pre-existing point-symmetric condensations in the AGB wind, a fact which would imply a quite peculiar mass-loss geometry from the giant progenitor. In the case of NGC 5882, the lack of symmetry in the distribution of the observed low-ionization structures makes it possible that they are the result of in situ instabilities.Comment: 20 pages including 1 table and 6 figures. ApJ accepted. Also available at http://andromeda.roque.ing.iac.es/~sanchez/ingpub/index2000.htm