arXiv subjects

Paola Mazzei

Publications and source records attributed to Paola Mazzei.

At least 19 recordsLinked to original sources

arXiv2022

Insights into the evolution of five isolated galaxies

The galaxy evolution is believed to be conditioned by the environment. Isolated galaxies or galaxies in poor groups are an excellent laboratory to study evolutionary mechanisms where effects of the environment are minimal. We present new {\it Swift}-{\tt UVOT} data in six filters, three in the ultraviolet (UV), of five isolated galaxies aiming at shedding light into their evolution. For all of our targets we present new UV integrated fluxes and for some of them also new UBV magnitudes. Our observations allow us to improve their multi-wavelength spectral energy distributions extending it over about 3 orders of magnitude in wavelength. We exploit our smooth-particle hydro-dynamical simulations with chemo-photometric implementation anchored, a posteriori, to the global multi-wavelength properties of our targets, to give insight into their evolution. Then we compare their evolutionary properties with those previously derived for several galaxies in groups. The evolution of our targets is driven by a merger occurred several Gyrs ago, in the redshift range $0.5\leq z \leq 4.5$, not unlike what we have already found for galaxies in groups. The merger shapes the potential well where the gas is accreting driving the star formation rate and the galaxy evolution. Isolated galaxies should not have suffered from interactions for at least 3\,Gyr. However, the initial merger is still leaving its signatures on the properties of our targets. Several rejuvenation episodes, triggered by {\it in situ} accretion, are highlighted. Moreover, jelly-fish morphologies appear as these galaxies achieve their maximum star formation rate, before their quenching phase.

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arXiv2021

Linear Spectropolarimetric Analysis of Fairall 9 with VLT/FORS2

The quasar Main Sequence (MS) appears to be an incredibly powerful tool to organize the diversity in large samples of type-1 quasars but the most important physical parameters governing it are still unclear. Here we investigate the origin of the broadening and of a defining feature of Population B sources: a strong redward asymmetry of the Balmer emission lines. We focus on a prototypical source, Fairall 9. Spectropolarimetric data of the Fairall 9 broad H$β$ and H$α$ profiles allowed for a view of the geometric and dynamical complexity of the line emitting regions. Measurements (1) provided evidence of rotational motion; (2) were helpful to test the presence of polar and equatorial scatterers, and their association with non-virial motions.

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arXiv2019

Investigating early-type galaxy evolution with a multi-wavelength approach. III. Insights from SPH simulations with chemo-photometric implementation

We are exploring galaxy evolution in low density environments exploiting smooth particle hydrodynamic simulations including chemo-photometric implementation. From a large grid of simulations of galaxy encounters and mergers starting from triaxial halos of gas e dark matter, we single out the simulations matching the global properties of our targets. These simulations are used to give insights into their evolution. We focus on 11 early-type galaxies selected because of their nearly passive stage of evolution in the nuclear region. However, a variety of UV features are detected in more than half of these galaxies. We find no significant differences in the formation mechanisms between galaxies with or without UV features. Major and minor mergers are able to reproduce their peculiar UV morphologies, galaxy encounters are more suitable for 'normal' early-type galaxies. Their star formation rate self-quenches several Gyr later the merger/encounter occurred, via gas exhaustion and stellar feedback, moving the galaxy from blue to red colors, driving the galaxy transformation. The length of the quenching is mass dependent and lasts from 1 to 5 Gyr or more in the less massive systems. All our targets are gas rich at redshift 1. Three of them assembled at most 40% of their current stellar mass at z>1, and seven assembled more than 50% between redshift 0.5 and 1. Their stellar mass grows with 4% by crossing the Green Valley before reaching their current position on the NUV-r vs. Mr diagram.

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arXiv2018

Spectropolarimetry of Galactic stars with anomalous extinction sightlines

Highly reddened type Ia Supernovae (SNe Ia) with low total-to-selective visual extinction ratio values, $R_V$, also show peculiar linear polarization wavelength dependencies with peak polarizations at short wavelengths ($λ_{max} \lesssim 0.4 μm$). It is not clear why sightlines to SNe Ia display such different continuum polarization profiles from interstellar sightlines in the Milky Way with similar $R_V$ values. We investigate polarization profiles of a sample of Galactic stars with low $R_V$ values, along anomalous extinction sightlines, with the aim to find similarities to the polarization profiles that we observe in SN Ia sightlines. We undertook spectropolarimetry of 14 stars, and used archival data for three additional stars, and run dust extinction and polarization simulations to infer a simple dust model that can reproduce the observed extinction and polarization curves. Our sample of Galactic stars with low $R_V$ values and anomalous extinction sightlines displays normal polarization profiles with an average $λ_{max} \sim 0.53 {μm}$, and is consistent within 3$σ$ to a larger coherent sample of Galactic stars from literature. Despite the low $R_V$ values of dust towards the stars in our sample, the polarization curves do not show any similarity to the continuum polarization curves observed towards SNe Ia with low $R_V$ values. There is a correlation between the best-fit Serkowski parameters $K$ and $λ_{max}$, but we did not find any significant correlation between $R_V$ and $λ_{max}$. Our simulations show that the $K-λ_{max}$ relationship is an intrinsic property of polarization. Furthermore, we have shown that in order to reproduce polarization curves with normal $λ_{max}$ and low $R_V$ values, a population of large (a $\geq 0.1 μm$) interstellar silicate grains must be contained in the dust's composition.

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arXiv2017

Galaxy evolution in groups. NGC 3447/NGC 3447A: the odd couple in LGG 225

Local Group Analogs (LGA) are galaxy associations dominated by few bright Spirals, reminiscent of the LG. The NGC3447/NGC3447A system, member of the LGG 225 group, a nearby LGA, is considered a physical pair: an intermediate luminosity late type spiral, NGC3447, and an irregular companion, NGC3447A, linked by a faint filament of matter. A ring-like structure in the NGC3447 outskirts is emphasised by UV observations. This work aims to contribute to the understanding of galaxy evolution in low density environments, favourable habitat to highly effective encounters. We performed a multi-wavelength analysis of the surface photometry of this system to derive spectral energy distribution and structural properties using UV and optical images. We also characterised the velocity field of the pair using new kinematic observations. All these data are used to constrain smooth particle hydrodynamic simulations with chemo-photometric implementation to shed light on the evolution of this system. Luminosity profiles are all consistent with the presence of a disc extending and including NGC3447A. The overall velocity field does not emphasise any significant rotation pattern, rather a small velocity gradient between NGC3447 and NGC3447A. Our simulation, detached from a large grid explored to best-fit the global properties of the system, suggests that this arises from an encounter between two halos of equal mass. NGC3447 and NGC3447A belong to the same halo, NGC3447A being a substructure of the same disk as NGC3447. The halo gravitational instability, enhanced by the encounter, fuels a long lived instability in this dark matter dominated disk, driving its morphology. This system may warn about a new class of "false pairs" and the potential danger of a misunderstanding of such objects in pair surveys that could produce a severe underestimate of the total mass of the system. (abridged)

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arXiv2016

Galaxy evolution in nearby galaxy groups. III. A GALEX view of NGC 5846, the largest group in the local universe

We explore the co-evolution of galaxies in nearby groups (V < 3000 km/s) with a multi-wavelength approach. We analyze GALEX far-UV (FUV) and near-UV (NUV) imaging and SDSS u,g,r,i,z data of groups spanning a large range of dynamical phases. We characterize the photometric properties of spectroscopically-confirmed galaxy members and investigate the global properties of the groups through a dynamical analysis. Here we focus on NGC 5846, the third most massive association of Early-Type Galaxies (ETG) after the Virgo and Fornax clusters. The group, composed of 90 members, is dominated by ETGs (about 80 per cent), and among ETGs about 40\% are dwarfs. Results are compared with those obtained for three groups in the LeoII cloud, which are radically different both in member-galaxy population and dynamical properties. The FUV-NUV cumulative colour distribution and the normalized UV luminosity function (LF) significantly differ due to the different fraction of late-type galaxy population. The UV LF of NGC 5846 resembles that of the Virgo cluster, however our analysis suggests that star-formation episodes are still occurring in most of the group galaxies, including ETGs. The NUV-i colour distribution, the optical-UV colour-colour diagram, and NUV-r vs. Mr colour-magnitude relation suggest that the gas contribution cannot be neglected in the evolution of ETG-type group members. Our analysis highlights that NGC~5846 is still in an active phase of its evolution, notwithstanding the dominance of dwarf and bright ETGs and its virialized configuration.

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arXiv2014

The UV window on counter rotating ETGs: insight from SPH simulations with chemo-photometric implementation

The Galaxy Evolution Explorer (GALEX) detected ultraviolet emission in about 50% of multi-spin early-type galaxies (ETGs), suggesting the occurrence of a recent rejuvenation episode connected to the formation of these kinematical features. With the aim at investigating the complex evolutionary scenario leading to the formation of counter rotating ETGs (CR-ETGs) we use our Smooth Particle Hydrodynamic (SPH) code with chemo-photometric implementation. We discuss here the UV evolutionary path of two CR-ETGs, NGC 3593 and NGC 5173, concurrently best fitting their global observed properties, i.e., morphology, dynamics, as well as their total B-band absolute magnitude and spectral energy distribution (SED) extended over three orders of magnitude in wavelength. These simulations correspond to our predictions about the target evolution which we follow in the color-magnitude diagram (CMD), near-UV (NUV) versus r-band absolute magnitude, as a powerful diagnostic tool to emphasize rejuvenation episodes.

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arXiv2014

The UV view of multi spin galaxies: insight from SPH simulations

The UV images of GALEX revealed that ~30% of Early Type Galaxies (ETG) show UV emission indicating a rejuvenation episode. In ETGs with multiple spin components this percentage increases at 50%. We present here the characteristics of this sample and our smooth particle hydrodynamic (SPH) simulations with chemo-photometric implementation that provide dynamical and morphological information together with the spectral energy distribution (SED) at each evolutionary stage. We show our match of the global properties of two ETGs (e.g. NGC 3626 and NGC 5173). For these galaxies we can trace their evolutionary path.

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arXiv2014

The ($NUV-r$) vs. $M_r$ as a tracer of early-type galaxies evolution in USGC U376 and LGG 225 groups

With the aim of tracing back the evolution of galaxies in nearby groups we use smooth particle hydrodynamical (SPH) simulations with chemo-photometric implementation. Here we focus on the evolution of the early-type members (Es and S0s, ETGs hereafter) in two groups, USGC U376 and LGG 225, both in the Leo cloud. We use the near-UV (NUV)-optical rest-frame $NUV-r$ versus $M_r$ color magnitude diagram to follow their evolution, from the blue cloud (BC) to the red sequence (RS), through the green valley (GV). ETGs brighter than $M_r=-21$ mag are older than 13 Gyr and spend up to 10 Gyr of their overall evolutionary time in the BC before they reach the RS migrating through the GV. Fainter ETGs are younger, of about 2 Gyr on average, and evolve for about 7-8 Gyr along the BC. The turn-off occurs at z ~ 0.3-0.4. Therefore these ETGs spend up to 3-5 Gyr crossing the GV; UGC 06324, the faintest ETG in the sample, still is in the GV. The mechanism driving their evolution is gravitational, due to merging and/or interaction. Our SPH simulations suggest that ETG members of these groups evolved toward the RS before and during the group collapse phase. This result is consistent with the dynamical analysis of both groups showing that they are not yet virialized.

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arXiv2010

Dust properties along anomalous extinction sightlines. II. Studying extinction curves with dust models

The large majority of extinction sight lines in our Galaxy obey a simple relation depending on one parameter, the total-to-selective extinction coefficient, Rv. Different values of Rv are able to match the whole extinction curve through different environments so characterizing normal extinction curves. In this paper more than sixty curves with large ultraviolet deviations from their best-fit one parameter curve are analyzed. These curves are fitted with dust models to shed light into the properties of the grains, the processes affecting them, and their relations with the environmental characteristics. The extinction curve models are reckoned by following recent prescriptions on grain size distributions able to describe one parameter curves for Rv values from 3.1 to 5.5. Such models, here extended down to Rv=2.0, allow us to compare the resulting properties of our deviating curves with the same as normal curves in a self-consistent framework, and thus to recover the relative trends overcoming the modeling uncertainties. Such curves represent the larger and homogeneous sample of anomalous curves studied so far with dust models. Results show that the ultraviolet deviations are driven by a larger amount of small grains than predicted for lines of sight where extinction depends on one parameter only. Moreover, the dust-to-gas ratios of anomalous curves are lower than the same values for no deviating lines of sight. Shocks and grain-grain collisions should both destroy dust grains, so reducing the amount of the dust trapped into the grains, and modify the size distribution of the dust, so increasing the small-to-large grain size ratio. Therefore, the extinction properties derived should arise along sight lines where shocks and high velocity flows perturb the physical state of the interstellar medium living their signature on the dust properties. (Abridged version)

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arXiv2008

Bars driven by the Cosmology in stellar-gaseous disks

We present the first attempt to analyse the growth of the bar instability in stellar-gaseous disks evolving in a fully consistent cosmological scenario. We explored the role of the cosmology on pure stellar disks with different mass embedded in a cosmological dark matter halo. We deepened such a study by analysing the impact of different gas fractions and of the star formation onset. We found that in all these cases, the stellar bar arising inside the less massive disks, i.e., dark matter (DM)-dominated disks, is still living at redshift zero even if the gas fraction exceeds half of the disk mass. Such a bar is a genuine product of the cosmology. However, in the most massive disks there is a threshold value for their gas percentage and lower limit for the central gas concentration able to destroy the bar when the star formation rate is switched off. On the other hand in the simulations with star formation the central mass concentration of gas and of the new stars has a mild action on the ellipticity of the bar but is not able to destroy it; at z=0 the stellar bar strength is enhanced by the star formation. Even if our results qualitatively agree with the classical ones, i.e. with criteria concerning bar instability derived outside the cosmological framework, the same criteria cannot be validated for the DM-dominated disks.

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arXiv2008

Star formation and bar instability in cosmological haloes

This is the third of a series of papers presenting the first attempt to analyze the growth of the bar instability in a consistent cosmological scenario. In the previous two articles we explored the role of the cosmology on stellar disks, and the impact of the gaseous component on a disk embedded in a cosmological dark matter halo. The aim of this paper is to point out the impact of the star formation on the bar instability inside disks having different gas fractions. We perform cosmological simulations of the same disk-to-halo mass systems as in the previous works where the star formation was not triggered. We compare the results of the new simulations with the previous ones to investigate the effect of the star formation by analysing the morphology of the stellar components, the bar strength, the behaviour of the pattern speed. We follow the gas and the central mass concentration during the evolution and their impact on the bar strength. In all our cosmological simulations a stellar bar, lasting 10 Gyr, is still living at z=0. The central mass concentration of gas and of the new stars has a mild action on the ellipticity of the bar but is not able to destroy it; at z=0 the stellar bar strength is enhanced by the star formation. The bar pattern speed is decreasing with the disk evolution.

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arXiv2005

Bar instability in cosmological halos

Aims: We want to investigate the growth of bar instability in stellar disks embedded in a suitable dark matter halo evolving in a fully consistent cosmological framework. Methods: We perform seven cosmological simulations to emphasise the role of both the disk-to-halo mass ratio and of the Toomre parameter, Q, on the evolution of the disk.We also compare our fully cosmological cases with corresponding isolated simulations where the same halo, is extracted from the cosmological scenario and evolved in physical coordinates. Results: A long living bar, lasting about 10 Gyr, appears in all our simulations. In particular, disks expected to be stable according to classical criteria, form indeed weak bars. We argue that such a result is due to the dynamical properties of our cosmological halo which is far from stability and isotropy, typical of the classical halos used in literature; it is dynamically active, endowed of substructures and infall. Conclusions: At least for mild self-gravitating disks, the study of the bar instability using isolated isotropic halos, in gravitational equilibrium, can lead to misleading results. Furthermore, the cosmological framework is needed for quantitatively investigating such an instability.

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arXiv2004

Dark and luminous matter connections. Towards understanding galaxy evolution

In this review we outline the major points of ab-initio cosmological models focusing on some galaxy evolution unresolved problems. In particular our knowledge of the star formation rate which leads galaxy evolution, i.e. luminosity, colors and dust enrichment, is still very poor. Smoothed particle hydrodynamic simulations including chemo-photometric evolutionary population synthesis models of isolated collapsing systems endowed with triaxial dark matter halos, gas and the star formation switched on, are a useful tool to shed light on several open questions. This approach, which allows a greater particle resolution than a fully consistent cosmological scenario, gives us important insights into connections between dark and luminous matter. Both the initial properties of the halo, as so as its geometry and dynamical state, and total mass of the system, drive the galaxy formation and evolution. In our simple framework spiral galaxies arise only in systems with both a total mass less than 1.e12 solar masses and a critical value of the baryonic-to-total-mass ratio, around its cosmological value, 0.1. For the same value of such a ratio more massive systems host more luminous and redder galaxies, as a consequence of the stronger burst of star formation arising into their halos earlier on. Moreover the star formation does not switch on in the less massive DM halos so that the critical mass to entail a luminous system is 1.e11 solar masses. For a given total mass, higher values of the baryonic-to-total-mass ratio provide galaxies with lower rotational support so that no constraints to the total mass of the system hosting an elliptical galaxy have been derived.

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arXiv2003

Abundances for metal-poor stars with accurate parallaxes II. alpha-elements in the halo

Abundances for alpha-elements and Fe in about 150 field subdwarfs and early subgiants with accurate parallaxes and kinematic data are used to discuss the run of abundance ratios in metal-poor stars in the solar neighborhood. Based on kinematics, we separated stars into two populations: the first one has a positive velocity of rotation around the galactic center, and it is likely to be related to the dissipational collapse of the galaxy; the second one has either negligible or negative rotational velocity, and it is likely related to an accretion component. The two populations show a large overlap in metallicity. However, they show distinct chemical properties. For the first population we found that there are close correlations (with small scatters around) of the rotational velocity with metallicity and with the Fe/alpha abundance ratio: this might be a signature of a not very fast collapse of the progenitor clouds, with enough time for a significant contribution by SNe Ia, although this result needs to be confirmed by a 3-D/non-LTE study. On the other side, the second population exhibits a larger scatter in both the above mentioned relations, and on average, a larger Fe/alpha ratio at a given metallicity, suggesting a larger scatter in ages. We argue that the lack of stars with moderate rotational velocities and high Fe/alpha abundance ratios is due to the short merging time for protogalactic clouds with prograde motion, while the presence of a group of counter-rotating stars with this characteristics indicates a much longer typical lifetimes for protogalactic fragments having such a motion. Finally, we found that perigalactic distances correlate with the Fe/alpha abundance ratios better than the apogalactic distances.

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arXiv2000

The Effect of Dust on Photometric Redshift Measurement; A Self-consistent Technique

A new method is developed for estimating photometric redshifts to galaxies, using realistic template SEDs, extending over four decades in wavelength (i.e. from 0.05 micron to 1 mm). The template SEDs are constructed for four different spectral types of galaxies (elliptical, spiral, irregular and starburst), satisfying the following characteristics: a). they are normalised to produce the observed colours of galaxies at z ~ 0; b). incorporate the chemo-photometric spectral evolution of galaxies of different types, in agreement with the observations; c). allow treatment of dust contribution and its evolution with redshift, consistent with the spectral evolution model; d). include absorption and re-emission of radiation by dust and hence, realistic estimates of the far-infrared radiation; e). include correction for inter-galactic absorption by Lyman continuum and Lyman forest. Using these template SEDs, the photometric redshifts are estimated to an accuracy of ~ 0.11. The effect on the estimated photometric redshifts, due to assumptions in the evolutionary population synthesis models, are investigated and discussed. The simultaneous and self-consistent modelling of both the photometric and chemical evolution of galaxies and the effect of dust, makes this technique particularly useful for high redshift galaxies. Moreover, since the template SEDs (at different redshifts) cover the range from UV to far-infrared and sub-mm wavelengths, one could consistently use the optimised SEDs to estimate the contribution from individual galaxies to these wavelengths, where no observational data are available.

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arXiv1997

Dust in high-z radio-loud AGN

We present continuum observations of a small sample of high-redshift, radio-loud AGN (radio galaxies and quasars) aimed at the detection of thermal emission from dust. Seven AGN were observed with IRAM and SEST at 1.25mm; two of them, the radio galaxies 1243+036 ($z \sim 3.6$) and MG1019+0535 ($z \sim 2.8$) were also observed at 0.8mm with the JCMT submillimetre telescope. Additional VLA observations were obtained in order to derive the spectral shape of the synchrotron radiation of MG1019+0535 at high radio frequencies. MG1019+0535 and TX0211$-$122 were expected to contain a large amount of dust based on their depleted Ly$α$ emission. The observations suggest a clear 1.25-mm flux density excess over the synchrotron radiation spectrum of MG1019+0535, suggesting the presence of thermal emission from dust in this radio galaxy, whereas the observations of TX0211$-$122 were not sensitive enough to meaningfully constrain its dust content. On the other hand, our observations of 1243+036 provide a stringent upper limit on the total dust mass of $<10^8$ M$_{\odot}$. Finally, we find that the spectra of the radio-loud quasars in our sample ($2 < z < 4.5$) steepen between rest-frame radio and the far-infrared. We discuss the main implications of our results, concentrating on the dusty radio galaxy, MG1019+0535.

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arXiv1995

Dust in High Redshift Radio Galaxies and the Early Evolution of Spheroidal Galaxies

Several lines of evidence suggest that early-type galaxies might have been very dusty during their initial evolutionary stages, characterized by intense star formation activity. The radio selection has provided, by far, the richest samples of high-$z$ galaxies, most likely of early type, which may therefore yield crucial direct information on the period when the bulk of stars were born. In order to investigate the role of dust in these phases, we have analyzed recent observations of a number of high-$z$ radio galaxies in the framework of a self-consistent scenario for the evolution of early type galaxies. The available data can be fully accounted for by ``opaque'' models similar to that already used by Mazzei and De Zotti (1994a) to fit the spectrum of the hyperluminous galaxy IRAS~F$10214+4724$. However, there is still considerable latitude for models. Good fits can be obtained with galactic ages ranging from 0.05 to 2 Gyr. Crucial constraints may be provided by ground-based sub-mm measurements and by observations with the forthcoming Infrared Space Observatory (ISO).

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