arXiv subjects

P. Mazzei

Publications and source records attributed to P. Mazzei.

34 records · Page 2Linked to original sources

arXiv2008

Revisiting the formation History of the minor-axis dust lane galaxy NGC1947

In this paper we present a detailed study of the peculiar early-type galaxy NGC1947. The main goal of this work is to constrain the dynamical status and the formation history of NGC1947 by comparing the observed properties with the predictions derived from different galaxy formation scenarios. To this aim, we derived the photometric and kinematical properties of NGC1947. Due to the presence of an extended dust-lane, which crosses the galaxy center along the photometric minor axis, we used near-infrared images (J and K bands) to derive an accurate analysis of the stellar light distribution. Optical images (in the V and R bands) are used to derive the color profiles and color maps to study the structure of the dust-lane. The observed kinematics confirm the presence of two components with decoupled angular momentum: gas and dust rotate along the minor axis, while the rotation velocities of the stars are observed along the major axis. The complex structure observed in NGC1947 support the hypothesis that some kind of interactions happened in the evolution of this object. We analyzed two alternatives: a merging process and an accretion event. We discussed how the observed properties strongly suggest that the decoupled ring of gas and dust have been accreted from outside.

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arXiv2007

Evolution of stellar-gaseous disks in cosmological haloes

We explore the growth and the evolution of the bar instability in stellar-gaseous disks embedded in a suitable dark matter halo evolving in a fully consistent cosmological framework. The aim of this paper is to point out the impact of different gas fractions on the bar formation, inside disks of different disk-to-halo mass ratio, and the role of the cosmological framework. We perform cosmological simulations with the same disk-to-halo mass ratios as in a previous work where the gas was not taken into account. We compare results of the new simulations with the previous ones to investigate the effect of the gas by analysing the morphology of the stellar and gaseous components, the stellar bar strength and the behaviour of its pattern speed. In our cosmological simulations, inside dark-matter dominated disks, a stellar bar, lasting 10 Gyr, is still living at z=0 even if the gaseous fraction exceeds half of the disk mass. However, in the most massive disks we find a threshold value (0.2) of the gas fraction able to destroy the bar. The stellar bar strength is enhanced by the gas and in the more massive disks higher gas fractions increase the bar pattern speed.

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arXiv2006

A multi--wavelength study of the IRAS Deep Survey galaxy sample II. The far-IR properties

We derive the 60μlocal LF to sensitivity levels 10 times deeper than before, to investigate evolutionary effects up to a redshift of 0.37, and, using the 60/15μbi-variate method, the poorly known 15μlocal LF of galaxies. We exploited our ISOCAM observations of the IRAS Deep Survey (IDS) fields (Hacking and Houck 1987), to correct the $60mu fluxes for confusion effects and observational biases. We find indications of a significant incompleteness of the IDS sample, still one of the deepest far-IR selected galaxy samples, below \simeq 80mJy (Mazzei et al. 2001). We have reliable identifications and spectroscopic redshifts for 100% of a complete subsample comprising 56 sources with S(60mu(m))> 80mJy. With our spectroscopic coverage we construct the 60mu LF for a sample complete down to 80 mJy. This LF extends over three orders of magnitude in luminosity, from 9 up to more than 12 in log(L_(60)/L_(\odot)). Despite the fact that the redshift range of our sample exceeds z=0.3, the V/V_{max} test gives =0.51\pm 0.06, consistent with a uniform distribution of sources. A more direct test, whereby the LF was measured in each of four different redshift intervals, does not point out any signature of evolution. On the other hand, the rest--frame 15μlocal LF we derive, extends up to log(L_{15}/L_{\odot})=12 and predicts 10 times more sources at log(L_{15}/L_{\odot})=11 than are seen by Pozzi et al. (2004).

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arXiv2001

Formation of Spheroidal Galaxies: The Sub-MM View

The intensity of the Cosmic Far-IR Background and the strong evolution of galaxies in the far-IR to mm wavelength range demonstrate that the bulk of starlight emitted during the early phases of galaxy evolution was reprocessed by dust. Therefore, the optical view of the galaxy formation process is highly incomplete and biased, and must be complemented with far-IR/sub-mm observations. We review the impact of sub-mm surveys on our understanding of the evolutionary history of spheroidal galaxies. A recent model, bringing into play also the inter-relationships between formation and early evolution of spheroidal galaxies and quasars, is described and some implications are outlined.

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arXiv2001

The impact of bars on the mid-infrared dust emission of spiral galaxies: global and circumnuclear properties

We study the mid-infrared properties of a sample of 69 nearby spiral galaxies, selected to avoid Seyfert activity contributing a significant fraction of the central energetics, or strong tidal interaction, and to have normal infrared luminosities. These observations were obtained with ISOCAM, which provides an angular resolution of the order of 10 arcsec (half-power diameter of the point spread function) and low-resolution spectro-imaging information. Between 5 and 18 microns, we mainly observe two dust phases, aromatic infrared bands and very small grains, both out of thermal equilibrium. On this sample, we show that the global F15/F7 colors of galaxies are very uniform, the only increase being found in early-type strongly barred galaxies, consistent with previous IRAS studies. The F15/F7 excesses are unambiguously due to galactic central regions where bar-induced starbursts occur. However, the existence of strongly barred early-type galaxies with normal circumnuclear colors indicates that the relationship between a distortion of the gravitational potential and a central starburst is not straightforward. As the physical processes at work in central regions are in principle identical in barred and unbarred galaxies, and since this is where the mid-infrared activity is mainly located, we investigate the mid-infrared circumnuclear properties of all the galaxies in our sample. We show how surface brightnesses and colors are related to both the available molecular gas content and the mean age of stellar populations contributing to dust heating. Therefore, the star formation history in galactic central regions can be constrained by their position in a color-surface brightness mid-infrared diagram.

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arXiv2001

An atlas of mid-infrared dust emission in spiral galaxies

We present maps of dust emission at 7 microns and 15 microns/7 microns intensity ratios of selected regions in 43 spiral galaxies observed with ISOCAM. This atlas is a complement to studies based on these observations, dealing with star formation in centers of barred galaxies and in spiral disks. It is accompanied by a detailed description of data reduction and an inventory of generic morphological properties in groups defined according to bar strength and HI gas content.

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arXiv1999

A Self-consistent Method for Estimating Photometric Redshifts

A new method is developed for estimating photometric redshifts, using realistic template SEDs, extending over four decades in wavelength (i.e from 0.05 $μm$ to 1 mm). The SEDs are constructed for four different spectral types of galaxies (elliptical, spiral, irregular and starburst) and satisfy the following characteristics: a). they are optimised to produce the observed colours of galaxies at $z\sim 0$; b). incorporate the chemo-photometric spectral evolution of galaxies of different types, in agreement with 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 $Δz = 0.11$. The degeneracy in the method and hence, the redshifts and spectral types, are explored via Monte Carlo simulations. The consistency of the technique is demonstrated by applying it on a UV selected sample of HDF galaxies and comparing the statistical results with those from other independent studies.

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arXiv1998

Extragalactic Source Counts and Contributions to the Anisotropies of the Cosmic Microwave Background. Predictions for the Planck Surveyor mission

We present predictions for the counts of extragalactic sources, the contributions to fluctuations and their spatial power spectrum in each channel foreseen for the Planck Surveyor (formerly COBRAS/SAMBA) mission. The contribution to fluctuations due to clustering of both radio and far--IR sources is found to be generally small in comparison with the Poisson term; however the relative importance of the clustering contribution increases and may eventually become dominant if sources are identified and subtracted down to faint flux limits. The central Planck frequency bands are expected to be ``clean'': at high galactic latitude (|b|>20), where the reduced galactic noise does not prevent the detection of the extragalactic signal, only a tiny fraction of pixels is found to be contaminated by discrete extragalactic sources. Moreover, removal of contaminating signals is eased by the substantial difference between their power spectrum and that of primordial fluctuations.

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arXiv1997

Source Counts and Background Radiation

Our present understanding of the extragalactic source counts and background radiation at infrared and sub-mm wavelengths is reviewed. Available count data are used to constrain evolutionary models of galaxies and Active Nuclei. The CIRB, on the other hand, provides crucial information on the integrated past IR emissivity, including sources so faint to be never accessible. The near-IR and sub-mm are suited to search for the CIRB. These cosmological windows are ideal to detect redshifted photons from the two most prominent broad emission features in galaxy spectra: the stellar photospheric 1 micron peak and the one at 100 micron due to dust re-radiation. The recently claimed detection of an isotropic diffuse component at 100-200 microns would support the evidence for strong cosmic evolution from $z=0$ to $z\sim 2$ of faint gas-rich late-type galaxies, as inferred from direct long-$λ$ counts. Furthermore, an equally intense CIRB flux measured in the wavelength range 200 to 500 $μm$ may be in support of models envisaging a dust-enshrouded phase during formation of spheroidal galaxies (e.g. Franceschini et al., 1994): the background spectrum at such long wavelengths would indicate an high redshift ($z>2-3$) for this active phase of star formation, implying a relevant constraint on structure formation scenarios. We argue that, given the difficulties for sky surveys in this spectral domain, only sporadic tests of these ideas will be achieved in the next several years. Only a mission like FIRST, in combination with large mm arrays and optical telescopes, will allow to thoroughly investigate, via photometric and spectroscopic surveys, these IR-bright early phases in the evolution of galaxies and AGNs.

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arXiv1996

Observability of Early Evolutionary Phases of Galaxies at mm Wavelengths

Several lines of evidence and theoretical arguments suggest that a large fraction of starlight is absorbed by interstellar dust and re-radiated at far-IR wavelengths, particularly during early evolutionary phases of early type galaxies, which may even, under some circumstances, experience an optically thick phase. Therefore far-IR to mm observations are crucial to understand the galaxy evolution. The strong K-correction makes surveys at mm wavelengths ideally suited for studying high-$z$ galaxies. The broad redshift range covered by mm surveys at sub-mJy flux limits offers a good chance for gaining important information also on the geometry of the Universe.

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arXiv1995

COSMOLOGICAL EVOLUTION OF EXTRAGALACTIC SOURCES IN THE INFRARED AND CONTRIBUTIONS TO THE BACKGROUND RADIATION

Infrared surveys provide essential insights on galaxy evolution. If near-IR studies suggest mild evolution of stellar populations with cosmic time, indications of a substantial evolution have been seen in the far-IR, although the available information is largely insufficient to delineate precise evolutionary properties. A consistent picture encompassing all the currently available data may be obtained assuming that dust extinction hides the early evolutionary phases of spheroidal galaxies in the optical band, while the corresponding dust re-radiation in the far-IR may have been, during the early evolutionary phases, orders of magnitude larger than today. Hyperluminous IRAS galaxies might be extreme examples of this situation. Additional indications that at least some spheroidal galaxies may have been very dusty during their early evolution are provided by recent data on high redshift radio galaxies and quasars. Galaxies are the likely dominant contributors to the IR background. However, in the framework of unified models for Active Galactic Nuclei, a large number of nuclei hidden by a dusty torus may be expected. Implications for the IR background are discussed.

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arXiv1994

The Extragalactic IR Background

Current limits on the intensity of the extragalactic infrared background are consistent with the expected contribution from evolving galaxies. Depending on the behaviour of the star formation rate and of the initial mass function, we can expect that dust extinction during early evolutionary phases ranges from moderate to strong. An example of the latter case may be the ultraluminous galaxy IRAS F$10214 + 4724$. The remarkable lack of high redshift galaxies in faint optically selected samples may be indirect evidence that strong extinction is common during early phases. Testable implications of different scenarios are discussed; ISO can play a key role in this context. Estimates of possible contributions of galaxies to the background under different assumptions are presented. The COBE/FIRAS limits on deviations from a blackbody spectrum at sub-mm wavelengths already set important constraints on the evolution of the far-IR emission of galaxies and on the density of obscured (``Type 2'') AGNs. A major progress in the field is expected at the completion of the analysis of COBE/DIRBE data.

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arXiv1994

Far-IR Properties of Early Type Galaxies

We have investigated the IRAS colours and the far-IR to optical luminosity ratios of a complete sample of elliptical's and S0's brighter than $B_T = 12$. On the average, elliptical galaxies emit in the far-IR less than 1\% of their bolometric luminosity, while S0's are about a factor of three brighter in the far-IR. On the average, the photospheric emission of red giant stars can account for 50--60\% of the $12\mic$ flux from early type galaxies; the contribution from diffuse dust at this wavelength is $< 10\%$ in the case of ellipticals,and may amount to 20--40\% for S0's. An additional, $\sim 30--40\%$, contribution from circumstellar emission from evolved giants with mass loss (particularly OH/IR stars) seems to be required in the case of ellipticals. This suggests a small but significant star formation activity in these galaxies at a look-back time of 1--$2\,$Gyr, corresponding to about 10\% of that typical of a disk galaxy having the same V-band luminosity. As for S0's, the larger diffuse dust emission may swamp to some extent that of circumstellar dust, which is indicated to be, on the average, $\lsim 20\%$. The weak emission from diffuse interstellar dust, detected mostly at $60\mic$ and $100\mic$, has color temperatures similar to those of disk galaxies; as in that case of the latter, a warm dust component is suggested, associated to star-forming regions. The implied star formation would be a few percent of that of disk galaxies of similar V-band luminosity and could account for a fraction of the observed UV branch of early type galaxies.

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arXiv1994

A Model for the Spectral Energy Distribution of the Ultraluminous Galaxy IRAS F10214+4724

If indeed early type galaxies used up most of their gas to form stars in a time short compared to their collapse time and if a roughly constant fraction of metals is locked up in dust grains, these galaxies may easily become opaque to starlight and emit most of their luminosity in the far-IR. The corresponding spectral energy distribution matches remarkably well the observed continuum spectrum of the ultraluminous galaxy IRAS F$10214+4724$ from UV to sub-mm wavelengths, i.e. over almost four decades in frequency, for a galactic age $\lsim 1\,$Gyr. The bolometric luminosity in this model is $\simeq 2.7\times 10^{14}\Lsol$ ($H_0 =50\,\hbox{km}\,\hbox{s}^{-1} \,\hbox{Mpc}^{-1}$, $Ω=1$), i.e. somewhat lower than implied by previous models. In the present framework, the bolometric luminosity of the galaxy is expected to decrease by a factor $\gsim 30$ during the subsequent evolution.

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arXiv1993

Models for the Evolution of the Spectral Energy Distribution of Elliptical Galaxies from UV to Far--IR Wavelengths

We have worked out evolutionary synthesis models of the broad-band spectral energy distribution of elliptical galaxies over the whole frequency range from UV to far--IR. Internal extinction and far--IR re--emission by interstellar dust have been taken into account in a self--consistent way. Diffuse dust emission has been modelled in terms of two components: warm dust, located in regions of high radiation intensity, and cold dust, heated by the general radiation field. Emission from circumstellar dust clouds at different galactic ages was also taken into account. The models reproduce well the present average broad--band spectrum of nearby ellipticals over about four decades in frequency. Under the assumption of a dust--to--gas ratio proportional to the metallicity, the fraction of bolometric luminosity coming out at far-IR wavelengths strongly evolves during the galaxy lifetime, ranging from very low local values ($\lsim 0.5\%$) to $\sim 30\%$ or more in the first billion years. Some models even imply that early phases are optically thick; these models provide an excellent fit of the observed spectral energy distribution of the high redshift galaxy IRAS F10214$+$4724. Far--IR observations may thus play a key role in investigating the early evolution of elliptical galaxies. A strong far-IR evolution of early-type galaxies might be a crucial ingredient to explain the deep $60\mic$ IRAS counts.

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arXiv1993

Background Radiation

We present a short overview on the extragalactic background radiation from radio to X-rays, with an eye to the relation to galaxy formation and emphasizing on astrophysical backgrounds (as opposed to cosmological). As the radio background, the wealth of data on source counts make possible reliable estimations of the contribution from extragalactic sources. At 178 MHz we obtain an antenna temperature of about 22 K, with the 60% of the flux contributed by radiogalaxies and quasars and the remaining part from sub-mJy radio sources. At high frequencies the compact sources, generally QSOs, dominate. An intense far-IR/sub-mm background is predicted if a large fraction of the hard X-ray Background (XRB) comes from starburst galaxies but this might face problems with the upper limits on the far-IR isotropic flux. To clarify the problem spectral measurements should be complemented with the analysis of small scale anisotropies. The flattening of the QSO counts at B=19.5 suggests that their contribution to the optical/near-IR background is small in comparison to that of galaxies. As for the XRB, a consisting picture obtains considering two AGN populations: a "soft X-ray spectrum" population and a "hard X-ray spectrum" one, mainly contributing to the soft and to the hard XRB respectively. A third population of extremely absorbed or of reflection dominated AGN could either be the dominant contributor of the XRB above 3 keV.

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