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E. Iodice

Publications and source records attributed to E. Iodice.

89 records · Page 5Linked to original sources
arXiv2013

VGS31b: a highly inclined ring along a filament in a void. Implication for the cold accretion

VGS31b is a highly-inclined ring galaxy found along a filament in a void (Kreckel et al. 2012). Detailed photometry, by using u, g, r, i, z SDSS images, has shown that the overall morphology of VGS31b is very tricky, due to (i) the presence of a highly inclined (72 deg) ring-like structure, which reaches the galaxy center tracing a "spiral-like" pattern, (ii) a one sided tail towards North-East and (iii) a bar in the central regions (Beygu et al. 2013). Such structure is reasonably the result of a "second event" in the evolution history of this galaxy, which could be a gravitational interaction with a companion galaxy or with the environment. The main aim of the present work is to address the most reliable formation scenario for this object, by comparing the observed properties, i.e. structure, baryonic mass, kinematics and chemical abundances, with the theoretical predictions. In particular, we have used archival spectroscopic data, to derive the metallicity in the ring: we found a very low, sub-solar average value of Z = 0.3 Zsun, comparable with other polar ring/disk galaxies, but lower than those measured for ordinary spirals of similar luminosity. The study of the chemical abundances in polar ring/disk galaxies and related objects has received an increasing attention in recent years, since it has revealed to be a key-parameter to disentangle among the formation scenarios suggested for this class of objects: major merging, tidal accretion or cold accretion. In the present work we check the cold accretion of gas through a "cosmic filament" as a possible scenario for the formation of the ring-like structure in VGS31b.

astro-ph.CO↗
arXiv2012

New photometric investigation of the double ringed galaxy ESO474-G26. Unveiling the formation scenario

We present a detailed photometric study of the peculiar double ringed galaxy ESO474-G26. Near-Infrared (NIR) and optical data have been used, with the main goal to constrain the formation history of ESO474-G26. NIR photometry is fundamental in this kind of study, because gives better constraints on the Spectral Energy Distribution (SED) and well traces the older stellar population of the galaxy. This galaxy presents a very complex structure, with two almost orthogonal rings, one in the equatorial and another in the polar plane, around an elliptical-like object. Due to the peculiar morphology of ESO474-G26, we used both NIR images (J and K bands) to derive accurate analysis of the stellar light distribution, and optical images (in the B, V and R bands) to derive color profiles and color maps to study the structure of the rings. The observational characteristic of ESO474-G26 are typical of galaxies which have experienced some kind of interactions during their evolution. We investigated two alternatives: a merging process and an accretion event.

astro-ph.CO↗
arXiv2011

Chemical abundances of the PRGs UGC7576 and UGC9796. I. Testing the formation scenario

The study of the chemical abundances of HII regions in polar ring galaxies and their implications for the evolutionary scenario of these systems has been a step forward both in tracing the formation history of the galaxy and giving hints on the mechanisms at work during the building of disk by cold accretion process. It's now important to establish whether such results are typical for the class of polar disk galaxies as whole. The present work aims at checking the cold accretion of gas through a "cosmic filament" as a possible scenario for the formation of the polar structures in UGC7576 and UGC9796. If these form by cold accretion, we expect the HII regions abundances and metallicities to be lower than those of same-luminosity spiral disks, with values of the order of Z ~ 1/10 Zsun, as predicted by cosmological simulations. We have used deep long-slit spectra, obtained with DOLORES@TNG in the optical wavelengths, of the brightest HII regions associated with the polar structures to derive their chemical abundances and star formation rate. We used the "Empirical methods", based on the intensities of easily observable lines, to derive the oxygen abundance 12+log(O/H) of both galaxies. Such values are compared with those typical for different morphological galaxy types of comparable luminosity. The average metallicity values for UGC7576 and UGC9796 are Z = 0.4 Zsun and Z = 0.1 Zsun respectively. Both values are lower than those measured for ordinary spirals of similar luminosity and UGC7576 presents no metallicity gradient along the polar structure. These data, toghether with other observed features, available for the two PRGs in previous works, are compared with the predictions of simulations of tidal accretion, cold accretion and merging, to disentangle between these scenarios.

astro-ph.CO↗
arXiv2010

Chemical abundances in the polar disk of NGC4650A: implications for cold accretion scenario

The aim of the present study is to test whether the cold accretion of gas through a "cosmic filament" Macciò et al. 2006 is a possible formation scenario for the polar disk galaxy NGC 4650A. If polar disks form from cold accretion of gas, the abundances of the HII regions may be similar to those of very late-type spiral galaxies, regardless of the presence of a bright central stellar spheroid, with total luminosity of few 10^9 Lsun. We use deep long slit spectra obtained with the FORS2 spectrograph at the VLT in the optical and near-infrared wavelength ranges for the brightest HII regions in the disk polar disk of NGC 4650A. The strongest emission lines ([OII] Hbeta, [OIII], Halpha) were used to derived oxygen abundances, metallicities and the global star formation rates for the disk. The deep spectra available allowed us to measure the Oxygen abundances (12 + log (O/H)) using the "Empirical method" based on intensities of the strongest emission lines, and the "Direct method", based on the determination of the electron temperature from the detection of weak auroral lines, as the [OIII] at 4363 Angstrom. The Oxygen abundance measured for the polar disk is then compared with those measured for different galaxy types of similar total luminosities, and then compared against the predictions of different polar ring formation scenarios. The average metallicity values for the polar disk in NGC 4650A is Z=0.2 Zsun, and it is lower that the values measured for ordinary spirals of similar luminosity. Moreover the gradient of the metallicity is flat along the polar disk major axis, which implies none or negligible metal enrichment from the stars in the older central spheroid. The low metallicity value in the polar disk NGC 4650A and the flat metallicity gradient are both consistent with a later infall of metal-poor gas, as expected in the cold accretion processes.

astro-ph.CO↗
arXiv2010

Polar Disk Galaxies as new way to study galaxy formation: the case of NGC4650A

NGC4650A is a polar disk galaxy: this is a peculiar object composed by a central spheroidal component, the host galaxy (HG), and an extended disk made up by gas, stars and dust, which orbits nearly perpendicular to the plane of the central galaxy. The existence of two decoupled components of the angular momentum let this object the ideal laboratory i) to study gravitational interactions and merging and ii) to constrain the 3D shape of its dark matter halo. In view of these applications, I will present two ongoing projects which aim to constrain i) the formation scenario for polar disks and ii) the dark halo content and shape, through a detailed analysis of the observed structure, metallicity and dynamics of NGC4650A.

astro-ph.GA↗
arXiv2009

GALEX UV properties of the polar ring galaxy MCG-05-07-001 and the shell galaxies NGC 1210 and NGC 5329

Systems of shells and polar rings in early-type galaxies are considered "bona fide" tracers of mass accretion and/or mergers. Their high frequency in low density environments suggests that such episodes could drive the evolution of at least a fraction of the early-type galaxy population. Their UV emission is crucial to test whether these galaxies host ongoing/recent star formation. We used far and near ultraviolet, optical, near infrared images, HI maps, and line strength indices to investigate the nuclear and outer regions of the galaxies as well as the regions where fine structures are present. The GALEX Near (NUV) and Far UV (FUV) images of MCG-05-07-001 and NGC 1210 show complex tidal tails and debris structures. The UV morphology of both galaxies appears so different from the optical one that the early-type classification may not apply. In both GALEX bands the polar ring of MCG-05-07-001 is the dominant feature, whereas an extended tidal tail dominates the FUV bands of NGC 1210. In MCG-05-07-001 and NGC 1210 there is a strong correlation between structures detected in the FUV and NUV bands and in HI. NGC 5329 does not show evidence of shells in the UV. We try to constrain the age of the accretion episode or merger which gave rise to the shells and polar rings with the aid of composite stellar populations that take the presence of dust into account. The presence of HI in both MCG-05-07-001 and NGC 1210 argues in favour of wet mergers. Models suggest the presence of very young stellar populations in MCG-05-07-001: the observations could be explained in the framework of a conspicuous burst of star formation that occurred <=1 Gyr ago and involved a large fraction of the galaxy mass. Our models suggest that also the nuclei of NGC 1210 and NGC 5329 could have been rejuvenated by an accretion episode about 2-4 Gyr ago. (abridged)

astro-ph.CO↗
arXiv2009

Metallicity of the polar disk in NGC4650A: constraints for cold accretion scenario

We used high resolution spectra in the optical and near-infrared wavelength range to study the abundance ratios and metallicities of the HII regions associated with the polar disk in NGC4650A, in order to put constraints on the formation of the polar disk through cold gas accretion along a filament; this might be the most realistic way by which galaxies get their gas. We have compared the measured metallicities for the polar structure in NGC4650A with those of different morphological types and we have found that they are similar to those of late-type galaxies: such results is consistent with a polar disk formed by accretion from cosmic web filaments of external cold gas.

astro-ph.CO↗
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.

astro-ph↗
arXiv2007

A kinematically decoupled component in NGC4778

We present a kinematical and photometrical study of a member, NGC4778, of the nearest (z=0.0137) compact group: Hickson 62. Our analysis reveals that Hickson 62a, also known as NGC4778, is an S0 galaxy with kinematical and morphological peculiarities, both in its central regions (r < 5'') and in the outer halo. In the central regions, the rotation curve shows the existence of a kinematically decoupled stellar component, offset with respect to the photometric center. In the outer halo we find an asymmetric rotation curve and a velocity dispersion profile showing a rise on the SW side, in direction of the galaxy NGC4776.

astro-ph↗
arXiv2006

Hickson 62.I. Kinematics of NGC4778

Detailed studies of the photometric and kinematical properties of compact groups of galaxies are crucial to understand the physics of galaxy interactions and to shed light on some aspects of galaxy formation and evolution. In this paper we present a kinematical and photometrical study of a member, NGC4778, of the nearest (z=0.0137) compact group: Hickson 62. Aims: The aim of this work was to investigate the existence of kinematical anomalies in the brightest group member, NGC4778 in order to constrain the dynamical status and the formation history of the group. Methods: We used long-slit spectra obtained with FORS1 at VLT, to measure line-of-sight velocity distributions by means of the Fourier Correlation Quotient method, and to derive the galaxy rotation curve and velocity dispersion profile. Results: Our analysis reveals that Hickson 62a, also known as NGC4778, is an S0 galaxy with kinematical and morphological peculiarities, both in its central regions (r < 5'') and in the outer halo. In the central regions, the rotation curve shows the existence of a kinematically decoupled stellar component, offset with respect to the photometric center. In the outer halo we find an asymmetric rotation curve and a velocity dispersion profile showing a rise on the SW side, in direction of the galaxy NGC4776. Conclusions: The nuclear counterrotation, the distorted kinematics in the outer halo and the X-ray properties of the group suggest that NGC4778 may be the product of a recent minor merger, more reliable with a small late-type galaxy.

astro-ph↗
arXiv2006

Stellar kinematics for the central spheroid in the Polar Disk Galaxy NGC4650A

We have obtained high angular resolution, high signal-to-noise spectra of the Calcium triplet absorption lines on the photometric axes of the stellar spheroid in the polar disk galaxy NGC4650A. Along the major axis, the observed rotation and velocity dispersion measurements show the presence of a kinematically decoupled nucleus, and a flat velocity dispersion profile. The minor axis kinematics is determined for the first time: along this direction some rotation is measured, and the velocity dispersion is nearly constant and slightly increases at larger distances from the center. The new high resolution kinematic data suggest that the stellar component in NGC4650A resembles a nearly-exponential oblate spheroid supported by rotation. The main implications of these results on the previous mass models for NGC4650A are discussed. Moreover, the new kinematic data set constraints on current models for the formation scenarios of Polar Ring Galaxies (PRGs), supporting a slow accretion rather then a secondary strong dissipative event.

astro-ph↗
arXiv2004

Photometric structure of the peculiar galaxy ESO 235-G58

We present the near-infrared and optical properties of the peculiar galaxy ESO 235-G58, which resembles a late-type ringed barred spiral seen close to face-on. However, the apparent bar of ESO 235-G58 is in reality an edge-on disk galaxy of relatively low luminosity. We have analyzed the light and color distributions of ESO 235-G58 in the NIR and optical bands and compared them with the typical properties observed for other morphological galaxy types, including polar ring galaxies. Similar properties are observed for ESO 235-G58, polar ring galaxies, and spiral galaxies, which leads us to conclude that this peculiar system is a polar-ring-related galaxy, characterized by a low inclined ring/disk structure, as pointed out by Buta & Crocker in an earlier study, rather than a barred galaxy.

astro-ph↗
arXiv2002

Polar Ring Galaxies and the Tully Fisher relation: implications for the dark halo shape

We have investigated the Tully-Fisher relation for Polar Ring Galaxies (PRGs), based on near infrared, optical and HI data available for a sample of these peculiar objects. The total K-band luminosity, which mainly comes from the central host galaxy, and the measured HI linewidth at 20% of the peak line flux density, which traces the potential in the polar plane, place most polar rings of the sample far from the Tully-Fisher relation defined for spiral galaxies, with many PRGs showing larger HI linewidths than expected for the observed K band luminosity. This result is confirmed by a larger sample of objects, based on B-band data. This observational evidence may be related to the dark halo shape and orientation in these systems, which we study by numerical modeling of PRG formation and dynamics: the larger rotation velocities observed in PRGs can be explained by a flattened polar halo, aligned with the polar ring.

astro-ph↗
arXiv2002

Near-Infrared photometry in the J, H and Kn bands for Polar Ring Galaxies: I. Data, structural parameters

We present new Near-Infrared (NIR) observations, in the J, H and Kn bands, for a sample of Polar Ring Galaxies (PRGs), selected from the Polar Ring Catalogue (Whitmore et al. 1990). Data were acquired with the CASPIR near-IR camera at the 2.3 m telescope of Mount Stromlo and Siding Spring Observatory. We report here on the detail morphological study for the central host galaxy and the polar structure in all PRGs of our sample. Total magnitudes, bulge-to-disk decomposition and structural parameters are computed for all objects. These data are crucial for an accurate modeling of the stellar population and the estimate of the star formation rates in the two components.

astro-ph↗
arXiv2002

Near-Infrared photometry in the J, H and Kn bands for Polar Ring Galaxies: II. Global Properties

We discuss the properties of the host galaxy and ring light distributions in the optical and near infrared bands for a sample of Polar Ring Galaxies (PRGs), presented in Paper I (Iodice et al. 2002, Paper I). The goal of this work is to test different formation scenarios for PRGs, proposed by different authors in the last decades, by comparing their predictions with these new data. The strategy is twofold: i) the integrated colors of the main components in these systems are compared with those of standard morphological galaxy types, to investigate whether differences in colors are caused by dust absorption or difference in stellar populations. We then derived an estimate of the stellar population ages in PRGs, which can be used to set constrains on the dynamical modeling and the time evolution of these systems; ii) we analyse the structural parameters of the host galaxy in order to understand whether this component is a standard early-type system as its morphology suggests, and the light distribution in the polar ring to measure its radial extension. These observational results indicate that the global properties of PRGs are better explained by dissipative merging of disks with un-equal masses as proposed by Bekki (1998), rather than the accretion-or stripping-of gas by a pre-existing early-type galaxy.

astro-ph↗
arXiv2001

The puzzle of the polar structure in NGC 4650A

This work presents new surface photometry and two-dimensional modeling of the light distribution of the Polar Ring Galaxy NGC 4650A, based on near-infrared (NIR) observations and high resolution optical imaging acquired during the Hubble Heritage program. The NIR and optical integrated colors of the S0 and the polar ring, and their scale parameters, are compared with those for standard galaxy morphological types. The polar structure appears to be a disk of a very young age, while the colors and light distribution of the host galaxy do not resemble that of a typical early-type system. We compare these observational results with the predictions from different formation scenarios for polar ring galaxies. The peculiarities of the central S0 galaxy, the polar disk structure and stellar population ages suggest that the polar ring galaxy NGC 4650A may be the result of a dissipative merger event, rather than of an accretion process.

astro-ph↗