arXiv subjects

E. Giallongo

Publications and source records attributed to E. Giallongo.

At least 73 records · Page 4Linked to original sources

arXiv2010

Physical and morphological properties of z~3 LBGs: dependence on Lyalpha line emission

We investigate the physical and morphological properties of LBGs at z ~2.5 to ~3.5, to determine if and how they depend on the nature and strength of the Lyalpha emission. We selected U-dropout galaxies from the z-detected GOODS MUSIC catalog, by adapting the classical Lyman Break criteria on the GOODS filter set. We kept only those galaxies with spectroscopic confirmation, mainly from VIMOS and FORS public observations. Using the full multi-wavelength 14-bands photometry, we determined the physical properties of the galaxies, through a standard spectral energy distribution fitting with the updated Charlot & Bruzual (2009) templates. We also added other relevant observations, i.e. the 24mu m observations from Spitzer/MIPS and the 2 MSec Chandra X-ray observations. Finally, using non parametric diagnostics (Gini, Concentration, Asymmetry, M_20 and ellipticity), we characterized the rest-frame UV morphology of the galaxies. We then analyzed how these physical and morphological properties correlate with the presence of the Lyalpha line in the optical spectra. We find that, unlike at higher redshift, the dependence of physical properties on the Lyalpha line is milder: galaxies without Lyalpha in emission tend to be more massive and dustier than the rest of the sample, but all other parameters, ages, SFRs, X-ray emission as well as UV morphology do not depend strongly on the presence of the line emission. A simple scenario where all LBGs have intrinsically high Lyalpha emission, but where dust and neutral hydrogen content (which shape the final appearance of the Lyalpha) depend on the mass of the galaxies, is able to reproduce the majority of the observed properties at z~3. Some modification might be needed to account for the observed evolution of these properties with cosmic epoch, which is also discussed.

astro-ph.CO↗

arXiv2010

Abell 611: I. weak lensing analysis with LBC

Aims. The Large Binocular Cameras (LBC) are two twin wide field cameras (FOV ~ 23'x 25') mounted at the prime foci of the 8.4m Large Binocular Telescope (LBT). We performed a weak lensing analysis of the z=0.288 cluster Abell 611 on g-band data obtained by the blue-optimized Large Binocular Camera in order to estimate the cluster mass. Methods. Due to the complexity of the PSF of LBC, we decided to use two different approaches, KSB and Shapelets, to measure the shape of background galaxies and to derive the shear signal produced by the cluster. Then we estimated the cluster mass with both aperture densitometry and parametric model fits. Results. The combination of the large aperture of the telescope and the wide field of view allowed us to map a region well beyond the expected virial radius of the cluster and to get a high surface density of background galaxies (23 galaxies/arcmin^2). This made possible to estimate an accurate mass for Abell 611. We find that the mass within 1.5 Mpc is: $(8\pm3)\times 10^{14} M_\odot$ from the aperture mass technique and $(5\pm1)\times 10^{14} M_\odot$ using the model fitting by a NFW mass density profile, for both Shapelets and KSB methods. This analysis demonstrates that LBC is a powerful instrument for weak gravitational lensing studies.

astro-ph.CO↗

arXiv2010

The end of the white dwarf cooling sequence in M 67

In this paper, we present for the first time a proper-motion-selected white dwarf (WD) sample of the old Galactic open cluster M 67, down to the bottom of the WD cooling sequence (CS). The color-magnitude diagram is based on data collected with the LBC-Blue camera at the prime focus of LBT. As first epoch data, we used CFHT-archive images collected 10 years before LBC data. We measured proper motions of all the identified sources. Proper motions are then used to separate foreground and background objects from the cluster stars, including WDs. Finally, the field-object cleaned WD CS in the V vs. B-I color-magnitude diagram is compared with the models. We confirm that the age derived from the location of the bottom of the WD CS is consistent with the turn off age.

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arXiv2009

Evidence for a fast evolution of the UV luminosity function beyond redshift 6 from a deep HAWK-I survey of the GOODS-S field

We perform a deep search for galaxies in the redshift range 6.5 1, Y-J<1.5 and Y-K<2. The other public data in the UBVRIJHK bands are used to reject possible low redshift interlopers. The output has been compared with extensive Monte Carlo simulations to quantify the observational effects of our selection criteria as well as the effects of photometric errors. We detect 7 high quality candidates in the magnitude range Y=25.5-26.7. This interval samples the critical range for M* at z>6 (M_1500 ~- 19.5 to -21.5). After accounting for the expected incompleteness, we rule out at a 99% confidence level a Luminosity Function constant from z=6 to z=7, even including the effects of cosmic variance. For galaxies brighter than M_1500=-19.0 we derive a luminosity density rho_UV=1.5^{+2.0}_{-0.9} 10^25 erg/s/Hz/Mpc3, implying a decrease by a factor 3.5 from z=6 to z~6.8. On the basis of our findings, we make predictions for the surface densities expected in future surveys surveys, based on ULTRA-VISTA, HST-WFC3 or JWST-NIRCam, evaluating the best observational strategy to maximise their impact.

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arXiv2009

GRB090426: the farthest short gamma-ray burst?

Aims. With an observed and rest-frame duration of < 2s and < 0.5s, respectively, GRB090426 could be classified as a short GRB. The prompt detection, both from space and ground-based telescopes, of a bright optical counterpart to this GRB offered a unique opportunity to complete a detailed study. Methods. Based on an extensive ground-based observational campaign, we obtained the spectrum of the optical afterglow of GRB090426, measuring its redshift and obtaining information about the medium in which the event took place. We completed follow-up observation of the afterglow optical light curve down to the brightness level of the host galaxy that we firmly identified and studied. We also retrieved and analyzed all the available high-energy data of this event, and compared the results with our findings in the optical. This represents one of the most detailed studies of a short-duration event presented so far. Results. The time properties qualify GRB090426 as a short burst. In this case, its redshift of z = 2.61 would be the highest yet found for a GRB of this class. On the other hand, the spectral and energy properties are more similar to those of long bursts. LBT late-time deep imaging identifies a star-forming galaxy at a redshift consistent with that of the GRB. The afterglow lies within the light of its host and shows evidence of local absorption.

astro-ph.HE↗

arXiv2009

Star formation and mass assembly in high redshift galaxies

We study the star formation and the mass assembly process of 0.3<=z<2.5 galaxies using their IR emission from MIPS 24um band. We used an updated version of the GOODS-MUSIC catalog, extended by the addition of mid-IR fluxes. We compared two different estimators of the Star Formation Rate: the total infrared emission derived from 24um, estimated using both synthetic and empirical IR templates, and the multiwavelength fit to the full galaxy SED. For both estimates, we computed the SFR Density and the Specific SFR. The two SFR tracers are roughly consistent, given the uncertainties involved. However, they show a systematic trend, IR-based estimates exceeding the fit-based ones as the SFR increases. We show that: a) at z>0.3, the SFR is well correlated with stellar mass, and this relationship seems to steepen with redshift (using IR-based SFRs); b) the contribution to the global SFRD by massive galaxies increases with redshift up to ~2.5, more rapidly than for galaxies of lower mass, but appears to flatten at higher z; c) despite this increase, the most important contributors to the SFRD at any z are galaxies of about, or immediately lower than, the characteristic stellar mass; d) at z~2, massive galaxies are actively star-forming, with a median SFR 300 Msun/yr. During this epoch, they assemble a substantial part of their final stellar mass; e) the SSFR shows a clear bimodal distribution. The analysis of the SFRD and the SSFR seems to support the downsizing scenario, according to which high mass galaxies have formed their stars earlier and faster than their low mass counterparts. A comparison with theoretical models indicates that they follow the global increase in the SSFR with redshift and predict the existence of quiescent galaxies even at z>1.5, but they systematically underpredict the average SSFR.

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arXiv2009

Wide and deep near-UV (360nm) galaxy counts and the extragalactic background light with the Large Binocular Camera

Deep multicolour surveys are the main tool to explore the formation and evolution of the faint galaxies which are beyond the spectroscopic limit with the present technology. The photometric properties of these faint galaxies are usually compared with current renditions of semianalytical models to provide constraints on the fundamental physical processes involved in galaxy formation and evolution, namely the mass assembly and the star formation. Galaxy counts over large sky areas in the near-UV band are important because they are difficult to obtain given the low efficiency of near-UV instrumentation, even at 8m class telescopes. A large instrumental field of view helps in minimizing the biases due to the cosmic variance. We have obtained deep images in the 360nm U band provided by the blue channel of the Large Binocular Camera at the prime focus of the Large Binocular Telescope. We have derived over an area of ~0.4 sq. deg. the galaxy number counts down to U=27 in the Vega system (corresponding to U=27.86 in the AB system) at a completeness level of 30% reaching the faintest current limit for this wavelength and sky area. The shape of the galaxy counts in the U band can be described by a double power-law, the bright side being consistent with the shape of shallower surveys of comparable or greater areas. The slope bends over significantly at U>23.5 ensuring the convergence of the contribution by star forming galaxies to the EBL in the near-UV band to a value which is more than 70% of the most recent upper limits derived for this band. We have jointly compared our near-UV and K band counts collected from the literature with few selected hierarchical CDM models emphasizing critical issues in the physical description of the galaxy formation and evolution.

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arXiv2009

Spatially Correlated Cluster Populations in the Outer Disk of NGC 3184

We use deep (~27.5 mag V-band point-source limiting magnitude) V- and U-band LBT imaging to study the outer disk (beyond the optical radius R_25) of the non-interacting, face-on spiral galaxy NGC 3184 (D = 11.1 Mpc; R_25 = 11.1 kpc) and find that this outer disk contains >1000 objects (or marginally-resolved 'knots') resembling star clusters with masses ~10^2 - 10^4 M_sun and ages up to ~1 Gyr. We find statistically significant numbers of these cluster-like knots extending to ~1.4 R_25, with the redder knots outnumbering bluer at the largest radii. We measure clustering among knots and find significant correlation to galactocentric radii of 1.5 R_25 for knot separations <1 kpc. The effective integrated surface brightness of this outer disk cluster population ranges from 30 - 32 mag arcsec^-2 in V. We compare the HI extent to that of the correlated knots and find that the clusters extend at least to the damped Lyman-alpha threshold of HI column density (2e20 cm^-2; 1.62 R_25). The blue knots are correlated with HI spiral structure to 1.5 R_25, while the red knots may be correlated with the outer fringes of the HI disk to 1.7 R_25. These results suggest that outer disks are well-populated, common, and long-lasting features of many nearby disk galaxies.

astro-ph.CO↗

arXiv2009

The Fraction of Quiescent Massive Galaxies in the Early Universe

Aims: The aim of this work is to collect a complete, mass--selected sample of galaxies with very low specific star formation rate, for a comparison with the prediction of recent theoretical models. Method: We use the 24/K flux ratio, complemented by the SED fitting to the full 0.35-8.0 mum spectral distribution, to select quiescent galaxies from z~0.4 to z~4 in the GOODS--MUSIC sample. Our observational selection can be translated into thresholds on the specific star formation rate SFR/M_*, that can be used to compare with the theoretical predictions. Results: We find that, in the framework of the well known global decline of the quiescent fraction with redshift, a non-negligible fraction ~15-20% of massive galaxies with very low specific star formation rate exists up to z~4, including a tail of "Red&Dead" galaxies with SFR/M_*<10^{-11}/yr. Recent theoretical models vary to a large extent in the prediction of the fraction of galaxies with very low specific star formation rates, and are unable to provide a global match to our data.

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arXiv2009

A Comprehensive Study of Large Scale Structures in the GOODS-SOUTH Field up to z \sim 2.5

The aim of this paper is to identify and study the properties and galactic content of groups and clusters in the GOODS-South field up to z\sim2.5, and to analyse the physical properties of galaxies as a continuous function of environmental density up to high redshift. We use the deep (z850\sim26), multi-wavelength GOODS-MUSIC catalogue, which has a 15% of spectroscopic redshifts and accurate photometric redshifts for the remaining fraction. On these data, we apply a (2+1)D algorithm, previously developed by our group, that provides an adaptive estimate of the 3D density field. We support our analysis with simulations to evaluate the purity and the completeness of the cluster catalogue produced by our algorithm. We find several high density peaks embedded in larger structures in the redshift range 0.4-2.5. From the analysis of their physical properties (mass profile, M200, \sigmav, LX, U-B vs. B diagram), we derive that most of them are groups of galaxies, while two are poor clusters with masses of few times 10^14 Mo. For these two clusters we find, from the Chandra 2Ms data, an X-ray emission significantly lower than expected from their optical properties, suggesting that the two clusters are either not virialised or gas poor. We also analyse the dependance on environment of galaxy colours, luminosities, stellar masses, ages and star formations. We find that galaxies in high density regions are, on average, more luminous and massive than field galaxies up to z\sim 2. The fraction of red galaxies increases with luminosity and with density up to z\sim 1.2. At higher z this dependance on density disappears. The variation of galaxy properties as a function of redshift and density suggests that a significant change occurs at z\sim 1.5-2. (abridged)

astro-ph.CO↗

arXiv2009

The isolated neutron star RBS1774 revisited. Revised XMM-Newton X-ray parameters and an optical counterpart from deep LBT-observations

We report optical B-band observations with the Large Binocular Telescope LBT of the isolated neutron star RBS1774. The stacked image with total exposure 2.5h reveals a candidate optical counterpart at mB = 26.96 +- 0.20 at position RA(2000) = 21:43:03.4, DEC(2000)} = +06:54:17:5, within the joint Chandra and XMM-Newton error circles. We analyse archival XMM-Newton observations and derive revised spectral and positional parameters. The predicted optical flux from the extrapolated X-ray spectrum is likely twice as high as reported before. The measured optical flux exceeds the extrapolated X-ray spectral flux by a factor ~40 (15 - 60 at 1sigma confidence). We interpret our detection and the spectral energy distribution as further evidence of a temperature structure over the neutron star's surface and present a pure thermal model reflecting both the SED and the pulsed fraction of the light curve.

astro-ph.GA↗

arXiv2009

Go Long, Go Deep: Finding Optical Jet Breaks for Swift-Era GRBs with the LBT

Using the 8.4m Large Binocular Telescope, we observed six GRB afterglows from 2.8 hours to 30.8 days after the burst triggers to systematically probe the late time behaviors of afterglows including jet breaks, flares, and supernova bumps. We detected five afterglows with Sloan r' magnitudes ranging from 23.0-26.3 mag. The depth of our observations allows us to extend the temporal baseline for measuring jet breaks by another decade in time scale. We detected two jet breaks and a third candidate, all of which are not detectable without deep, late time optical observations. In the other three cases, we do not detect the jet breaks either because of contamination from the host galaxy light, the presence of a supernova bump, or the intrinsic faintness of the optical afterglow. This suggests that the basic picture that GRBs are collimated is still valid and that the apparent lack of Swift jet breaks is due to poorly sampled afterglow light curves, particularly at late times.

astro-ph↗

arXiv2009

Uncertainties and Systematic Effects on the estimate of stellar masses in high z galaxies

We discuss the uncertainties and the systematic effects that exist in the estimates of the stellar masses of high redshift galaxies, using broad band photometry, and how they affect the deduced galaxy stellar mass function. We use at this purpose the latest version of the GOODS-MUSIC catalog. In particular, we discuss the impact of different synthetic models, of the assumed initial mass function and of the selection band. Using Charlot & Bruzual 2007 and Maraston 2005 models we find masses lower than those obtained from Bruzual & Charlot 2003 models. In addition, we find a slight trend as a function of the mass itself comparing these two mass determinations with that from Bruzual & Charlot 2003 models. As consequence, the derived galaxy stellar mass functions show diverse shapes, and their slope depends on the assumed models. Despite these differences, the overall results and scenario remains unchanged. The masses obtained with the assumption of the Chabrier initial mass function are in average 0.24 dex lower than those from the Salpeter assumption, at all redshifts, causing a shift of galaxy stellar mass function of the same amount. Finally, using a 4.5 um-selected sample instead of a Ks-selected one, we add a new population of highly absorbed, dusty galaxies at z\simeq 2-3 of relatively low masses, yielding stronger constraints on the slope of the galaxy stellar mass function at lower masses.

astro-ph.CO↗

arXiv2008

The physical properties of Lyalpha emitting galaxies: not just primeval galaxies?

We have analyzed a sample of LBGs from z =3.5 to z=6 selected from the GOODS-S field as B,V and i-dropouts, and with spectroscopic observations showing that they have the Lyalpha line in emission. Our main aim is to investigate their physical properties and their dependence on the emission line characteristics, to shed light on the relation between galaxies with Lyalpha emission and the general LBG population.The objects were selected from their continuum colors and then spectroscopically confirmed by the GOODS collaboration and other campaigns. From the spectra we derived the line flux and EW. We then used U-band to mid-IR photometry from GOODS-MUSIC to derive the physical properties of the galaxies, such as total stellar mass, age and so on, through standard SED fitting techniques.Although most galaxies are fit by young stellar populations, a small but non negligible fraction has SEDs that require considerably older stellar component, up to 1 Gyr. There is no apparent relation between age and EW: some of the oldest galaxies have large EW, and should be also selected in narrow band surveys. Therefore not all Lyalpha emitters are primeval galaxies in the very early stages of formation,as is commonly assumed. We also find a large range of stellar populations, with masses from 5x10^8 Msol to 5x10^10 Msol and SFR from few to 60 Msol/yr. Although there is no correlation between mass and EW, we find a significant lack of massive galaxies with high EW, which could be explained if the most massive galaxies were more dusty and/or contained more neutral gas than less massive objects. Finally we find that more than half of the galaxies contain small but non negligible amounts of dust: the mean E(B-V) and the EW are well correlated, although with a large scatter, as already found at lower redshift

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arXiv2008

The LBT Panoramic View on the Recent Star-Formation Activity in IC2574

We present deep imaging of the star-forming dwarf galaxy IC2574 in the M81 group taken with the Large Binocular Telescope in order to study in detail the recent star-formation history of this galaxy and to constrain the stellar feedback on its HI gas. We identify the star-forming areas in the galaxy by removing a smooth disk component from the optical images. We construct pixel-by-pixel maps of stellar age and stellar mass surface density in these regions by comparing their observed colors with simple stellar populations synthesized with STARBURST99. We find that an older burst occurred about 100 Myr ago within the inner 4 kpc and that a younger burst happened in the last 10 Myr mostly at galactocentric radii between 4 and 8 kpc. We analyze the stellar populations residing in the known HI holes of IC2574. Our results indicate that, even at the remarkable photometric depth of the LBT data, there is no clear one-to-one association between the observed HI holes and the most recent bursts of star formation in IC2574. The stellar populations formed during the younger burst are usually located at the periphery of the HI holes and are seen to be younger than the holes dynamical age. The kinetic energy of the holes expansion is found to be on average 10% of the total stellar energy released by the stellar winds and supernova explosions of the young stellar populations within the holes. With the help of control apertures distributed across the galaxy we estimate that the kinetic energy stored in the HI gas in the form of its local velocity dispersion is about 35% of the total stellar energy.

astro-ph↗

arXiv2008

The performance of the blue prime focus Large Binocular Camera at the Large Binocular Telescope

We present the characteristics and some early scientific results of the first instrument at the Large Binocular Telescope (LBT), the Large Binocular Camera (LBC). Each LBT telescope unit will be equipped with similar prime focus cameras. The blue channel is optimized for imaging in the UV-B bands and the red channel for imaging in the VRIz bands. The corrected field-of-view of each camera is approximately 30 arcminutes in diameter, and the chip area is equivalent to a 23x23 arcmin2 field. In this paper we also present the commissioning results of the blue channel. The scientific and technical performance of the blue channel was assessed by measurement of the astrometric distortion, flat fielding, ghosts, and photometric calibrations. These measurements were then used as input to a data reduction pipeline applied to science commissioning data. The measurements completed during commissioning show that the technical performance of the blue channel is in agreement with original expectations. Since the red camera is very similar to the blue one we expect similar performance from the commissioning that will be performed in the following months in binocular configuration. Using deep UV image, acquired during the commissioning of the blue camera, we derived faint UV galaxy-counts in a ~500 sq. arcmin. sky area to U(Vega)=26.5. These galaxy counts imply that the blue camera is the most powerful UV imager presently available and in the near future in terms of depth and extent of the field-of-view. We emphasize the potential of the blue camera to increase the robustness of the UGR multicolour selection of Lyman break galaxies at redshift z~3.

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arXiv2008

The structural properties and star formation history of Leo T from deep LBT photometry

We present deep, wide-field g and r photometry of the transition type dwarf galaxy Leo T, obtained with the blue arm of the Large Binocular Telescope. The data confirm the presence of both very young (<1 Gyr) as well as much older (>5 Gyr) stars. We study the structural properties of the old and young stellar populations by preferentially selecting either population based on their color and magnitude. The young population is significantly more concentrated than the old population, with half-light radii of 104+-8 and 148+-16 pc respectively, and their centers are slightly offset. Approximately 10% of the total stellar mass is estimated to be represented by the young stellar population. Comparison of the color-magnitude diagram (CMD) with theoretical isochrones as well as numerical CMD-fitting suggest that star formation began over 10 Gyr ago and continued in recent times until at least a few hundred Myr ago. The CMD-fitting results are indicative of two distinct star formation bursts, with a quiescent period around 3 Gyr ago, albeit at low significance. The results are consistent with no metallicity evolution and [Fe/H] ~ -1.5 over the entire age of the system. Finally, the data show little if any sign of tidal distortion of Leo T.

astro-ph↗

arXiv2008

The Blue Straggler population in the globular cluster M53 (NGC5024): a combined HST, LBT, CFHT study

We used a proper combination of multiband high-resolution and wide field multi-wavelength observations collected at three different telescopes (HST, LBT and CFHT) to probe Blue Straggler Star (BSS) populations in the globular cluster M53. Almost 200 BSS have been identified over the entire cluster extension. The radial distribution of these stars has been found to be bimodal (similarly to that of several other clusters) with a prominent dip at ~60'' (~2 r_c) from the cluster center. This value turns out to be a factor of two smaller than the radius of avoidance (r_avoid, the radius within which all the stars of ~1.2 M_sun have sunk to the core because of dynamical friction effects in an Hubble time). While in most of the clusters with a bimodal BSS radial distribution, r_avoid has been found to be located in the region of the observed minimum, this is the second case (after NGC6388) where this discrepancy is noted. This evidence suggests that in a few clusters the dynamical friction seems to be somehow less efficient than expected. We have also used this data base to construct the radial star density profile of the cluster: this is the most extended and accurate radial profile ever published for this cluster, including detailed star counts in the very inner region. The star density profile is reproduced by a standard King Model with an extended core (~25'') and a modest value of the concentration parameter (c=1.58). A deviation from the model is noted in the most external region of the cluster (at r>6.5' from the center). This feature needs to be further investigated in order to address the possible presence of a tidal tail in this cluster.

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