arXiv subjects

F. Mannucci

Publications and source records attributed to F. Mannucci.

At least 145 records · Page 8Linked to original sources

arXiv2009

LSD: Lyman-break galaxies Stellar populations and Dynamics. I: Mass, metallicity and gas at z~3.1

We present the first results of a project, LSD, aimed at obtaining spatially-resolved, near-infrared spectroscopy of a complete sample of Lyman-Break Galaxies at z~3. Deep observations with adaptive optics resulted in the detection of the main optical lines, such as [OII], Hbeta and [OIII], which are used to study sizes, SFRs, morphologies, gas-phase metallicities, gas fractions and effective yields. Optical, near-IR and Spitzer/IRAC photometry is used to measure stellar mass. We obtain that morphologies are usually complex, with the presence of several peaks of emissions and companions that are not detected in broad-band images. Typical metallicities are 10-50% solar, with a strong evolution of the mass-metallicity relation from lower redshifts. Stellar masses, gas fraction, and evolutionary stages vary significantly among the galaxies, with less massive galaxies showing larger fractions of gas. In contrast with observations in the local universe, effective yields decrease with stellar mass and reach solar values at the low-mass end of the sample. This effect can be reproduced by gas infall with rates of the order of the SFRs. Outflows are present but are not needed to explain the mass-metallicity relation. We conclude that a large fraction of these galaxies are actively creating stars after major episodes of gas infall or merging.

astro-ph.CO↗

arXiv2009

Type Ia supernova science 2010-2020

In the next decade Type Ia supernovae (SNe Ia) will be used to test theories predicting changes in the Dark Energy equation of state with time. Ultimately this requires a dedicated space mission like JDEM. SNe Ia are mature cosmological probes --- their limitations are well characterized, and a path to improvement is clear. Dominant systematic errors include photometric calibration, selection effects, reddening, and population-dependent differences. Building on past lessons, well-controlled new surveys are poised to make strides in these areas: the Palomar Transient Factory, Skymapper, La Silla QUEST, Pan-STARRS, the Dark Energy Survey, LSST, and JDEM. They will obviate historical calibrations and selection biases, and allow comparisons via large subsamples. Some systematics follow from our ignorance of SN Ia progenitors, which there is hope of determining with SN Ia rate studies from 0<z<4. Aside from cosmology, SNe Ia regulate galactic and cluster chemical evolution, inform stellar evolution, and are laboratories for extreme physics. Essential probes of SNe Ia in these contexts include spectroscopy from the UV to the IR, X-ray cluster and SN remnant observations, spectropolarimetry, and advanced theoretical studies. While there are an abundance of discovery facilities planned, there is a deficit of follow-up resources. Living in the systematics era demands deep understanding rather than larger statistics. NOAO ReSTAR initiative to build 2-4m telescopes would provide necessary follow-up capability. Finally, to fully exploit LSST, well-matched wide-field spectroscopic capabilities are desirable.

astro-ph.SR↗

arXiv2009

The supernova rate: a critical ingredient and an important tool

In this review I summarize the role of supernova rate as a critical ingredient of modern astrophysics, and as an important tool to understand SN explosions. Many years of active observations and theoretical modeling have produced several important results. In particular, linking SN rates with parent stellar populations has proved to be an important strategy. Despite these advances, the situation is far from clear, in particular for the SNe Ia.

astro-ph.SR↗

arXiv2008

LSD and AMAZE: the mass-metallicity relation at z>3

We present the first results on galaxy metallicity evolution at z>3 from two projects, LSD (Lyman-break galaxies Stellar populations and Dynamics) and AMAZE (Assessing the Mass Abundance redshift Evolution). These projects use deep near-infrared spectroscopic observations of a sample of ~40 LBGs to estimate the gas-phase metallicity from the emission lines. We derive the mass-metallicity relation at z$>$3 and compare it with the same relation at lower redshift. Strong evolution from z=0 and z=2 to z=3 is observed, and this finding puts strong constrains on the models of galaxy evolution. These preliminary results show that the effective oxygen yields does not increase with stellar mass, implying that the simple outflow model does not apply at z>3.

astro-ph↗

arXiv2008

AMAZE. I. The evolution of the mass-metallicity relation at z>3

We present initial results of an ESO-VLT large programme (AMAZE) aimed at determining the evolution of the mass-metallicity relation at z>3 by means of deep near-IR spectroscopy. Gas metallicities are measured, for an initial sample of nine star forming galaxies at z~3.5, by means of optical nebular lines redshifted into the near-IR. Stellar masses are accurately determined by using Spitzer-IRAC data, which sample the rest-frame near-IR stellar light in these distant galaxies. When compared with previous surveys, the mass-metallicity relation inferred at z~3.5 shows an evolution much stronger than observed at lower redshifts. The evolution is prominent even in massive galaxies, indicating that z~3 is an epoch of major action in terms of star formation and metal enrichment also for massive systems. There are also indications that the metallicity evolution of low mass galaxies is stronger relative to high mass systems, an effect which can be considered the chemical version of the galaxy downsizing. The mass-metallicity relation observed at z~3.5 is difficult to reconcile with the predictions of some hierarchical evolutionary models. Such discrepancies suggest that at z>3 galaxies are assembled mostly with relatively un-evolved sub-units, i.e. small galaxies with low star formation efficiency. The bulk of the star formation and metallicity evolution probably occurs once small galaxies are already assembled into bigger systems.

astro-ph↗

arXiv2008

Laser Guide Star Adaptive Optics without Tip-tilt

Adaptive optics (AO) systems allow a telescope to reach its diffraction limit at near infrared wavelengths. But to achieve this, a bright natural guide star (NGS) is needed for the wavefront sensing, severely limiting the fraction of the sky over which AO can be used. To some extent this can be overcome with a laser guide star (LGS). While the laser can be pointed anywhere in the sky, one still needs to have a natural star, albeit fainter, reasonably close to correct the image motion (tip-tilt) to which laser guide stars are insensitive. There are in fact many astronomical targets without suitable tip-tilt stars, but for which the enhanced resolution obtained with the Laser Guide Star Facility (LGSF) would still be very beneficial. This article explores what adaptive optics performance one might expect if one dispenses with the tip-tilt star, and in what situations this mode of observing might be needed.

astro-ph↗

arXiv2007

The evolution of the mass-metallicity relation at z~3

We present preliminary results of an ESO-VLT large programme (AMAZE) aimed at determining the evolution of the mass-metallicity relation at z~3 by means of deep near-IR spectroscopy. Gas metallicities and stellar masses are measured for an initial sample of nine star forming galaxies at z~3.3. When compared with previous surveys, the mass-metallicity relation inferred at z~3.3 shows an evolution significantly stronger than observed at lower redshifts. There are also some indications that the metallicity evolution of low mass galaxies is stronger relative to high mass systems, an effect which can be considered as the chemical version of the galaxy downsizing. The mass-metallicity relation observed at z~3.3 is difficult to reconcile with the predictions of some hierarchical evolutionary models. We shortly discuss the possible implications of such discrepancies.

astro-ph↗

arXiv2007

The supernova rate in local galaxy clusters

We report a measurement of the supernova (SN) rates (Ia and core-collapse) in galaxy clusters based on the 136 SNe of the sample described in Cappellaro et al. (1999) and Mannucci et al. (2005). Early-type cluster galaxies show a type Ia SN rate (0.066 SNuM) similar to that obtained by Sharon et al. (2007) and more than 3 times larger than that in field early-type galaxies (0.019 SNuM). This difference has a 98% statistical confidence level. We examine many possible observational biases which could affect the rate determination, and conclude that none of them is likely to significantly alter the results. We investigate how the rate is related to several properties of the parent galaxies, and find that cluster membership, morphology and radio power all affect the SN rate, while galaxy mass has no measurable effect. The increased rate may be due to galaxy interactions in clusters, inducing either the formation of young stars or a different evolution of the progenitor binary systems. We present the first measurement of the core-collapse SN rate in cluster late-type galaxies, which turns out to be comparable to the rate in field galaxies. This suggests that no large systematic difference in the initial mass function exists between the two environments.

astro-ph↗

arXiv2007

The assessment of the near infrared identification of Carbon stars. I. The Local Group galaxies WLM, IC 10 and NGC 6822

{The selection of AGB C and M stars from NIR colours has been done in recent years using adjustable criteria that are in needs of standardization if one wants to compare, in a coherent manner, properties of various populations.} We intend to assess the NIR colour technique to identify C and M stars. We compare the NIR colours of several C stars previously identified from spectroscopy or narrow band techniques in WLM, IC 10 and NGC 6822. We demonstrate that very few M stars have $(J-K)_0 > 1.4$ but a non negligible number of C stars are bluer than this limit. Thus, counts of M and C stars based on such limit do not produce pure samples. C/M ratios determined from NIR colours must be regarded as underestimates mainly because the M numbers include many warm C stars and also K stars if no blue limit is considered.

astro-ph↗

arXiv2007

Supernova rates and stellar populations

We discuss the results about the nature of type Ia Supernovae that can be derived by studying their rates in different stellar populations. While the evolution of SN photometry and spectra can constrain the explosion mechanism, the SN rate depends on the progenitor system. We review the current available data on rates as a function of parent galaxy color, morphology, star formation rate, radio luminosity and environment. By studying the variation of the rates with the color of the parent galaxy, a strong evidence was established that type Ia SNe come from both young and old stars. The dependence of the rates with the radio power of the parent galaxy is best reproduced by a bimodal distribution of delay time between the formation of the progenitor and its explosion as a SN. Cluster early-type galaxies show higher type Ia SN rate with respect to field galaxies, and this effect can be due either to traces of young stars or to differences in the delay time distribution.

astro-ph↗

arXiv2007

The bimodality of type Ia Supernovae

We comment on the presence of a bimodality in the distribution of delay time between the formation of the progenitors and their explosion as type Ia SNe. Two "flavors" of such bimodality are present in the literature: a "weak" bimodality, in which type Ia SNe must explode from both young and old progenitors, and a "strong" bimodality, in which about half of the systems explode within 10^8 years from formation. The "weak" bimodality is observationally based on the dependence of the rates with the host galaxy SFR, while the "strong" one on the different rates in radio-loud and radio-quiet early-type galaxies. We review the evidence for these bimodalities. Finally, we estimate the fraction of SNe which are missed by optical and near-IR searches because of dust extinction in massive starbursts.

astro-ph↗

arXiv2007

A galaxy overdensity at z=0.401 associated with an X-ray emitting structure of Warm-Hot Intergalactic Medium

We present the results of spectroscopic observations of galaxies associated with the diffuse X-ray emitting structure discovered by Zappacosta et al. (2002). After measuring the redshifts of 161 galaxies, we confirm an overdensity of galaxies with projected dimensions of at least 2 Mpc, determine its spectroscopic redshift in z=0.401+/-0.002, and show that it is spatially coincident with the diffuse X-ray emission. This confirms the original claim that this X-ray emission has an extragalactic nature and is due to the Warm-Hot Intergalactic Medium (WHIM). We used this value of the redshift to compute the temperature of the emitting gas. The resulting value depends on the metallicity that is assumed for the IGM, and is constrained to be between 0.3 and 0.6 keV for metallicities between 0.05 and 0.3 solar, in good agreement with the expectations from the WHIM.

astro-ph↗

arXiv2007

How many supernovae are we missing at high redshift?

Near-infrared and radio searches for core-collapse supernovae (CC SNe) in the local universe have shown that the vast majority of the events occurring in massive starburst are missed by the current optical searches as they explode in very dusty environments. Recent infrared observations have shown that the fraction of star-formation activity that takes place in very luminous dusty starbursts sharply increases with redshift and becomes the dominant star formation component at z>0.5. As a consequence, an increasing fraction of SNe are expected to be missed by high-redshift optical searches. We estimate that 5-10% of the local CC SNe are out of reach of the optical searches. The fraction of missing events rises sharply toward z=1, when about 30% of the CC SNe will be undetected. At z=2 the missing fraction will be about 60%. Correspondingly, for type Ia SNe, our computations provide missing fractions of 15% at z=1 and 35% at z=2. Such large corrections are crucially important to compare the observed SN rate with the expectations from the evolution of the cosmic star formation history, and to design the future SN searches at high redshifts.

astro-ph↗

arXiv2006

The Star Formation Density at z=7

Near-infrared VLT data of the GOODS-South area were used to look for galaxies at z=7 down to a limiting magnitude of (J+Ks)AB=25.5. No high-redshift candidates were detected, and this provides clear evidence for a strong evolution of the luminosity function between z=6 and z=7, i.e. over a time interval of only 170 Myr. Our constraints provide evidence of a significant decline in the total star formation rate at z=7, which must be less than 40% of that at z=3 and 40-80% of that at z=6. The resulting upper limit to the ionizing flux at z=7 is only marginally consistent with what is required to completely ionize the Universe.

astro-ph↗

arXiv2006

A NICMOS search for obscured Supernovae in starburst galaxies

The detection of obscured supernovae (SNe) in near-infrared monitoring campaigns of starburst galaxies has shown that a significant fraction of SNe is missed by optical surveys. However, the number of SNe detected in ground-based near-IR observations is still significantly lower than the number of SNe extrapolated from the FIR luminosity of the hosts. A possibility is that most SNe occur within the nuclear regions, where the limited angular resolution of ground-based observations prevents their detection. This issue prompted us to exploit the superior angular resolution of NICMOS-HST to search for obscured SNe within the first kpc from the nucleus of strong starbursting galaxies. A total of 17 galaxies were observed in SNAPSHOT mode. Based on their FIR luminosity, we expected to detect not less than ~12 SNe. However, no confirmed SN event was found. From our data we derive an observed nuclear SN rate <0.5 SN/yr per galaxy. The shortage of SN detections can be explained by a combination of several effects. The most important are: i) the existence of a strong extinction, A_V>11; ii) most SNe occur within the first 0.5" (which corresponds in our sample to about 500pc) where even NICMOS is unable to detect SN events.

astro-ph↗

arXiv2006

Evidence for strong evolution of the cosmic star formation density at high redshift

Deep HST/ACS and VLT/ISAAC data of the GOODS-South field were used to look for high-redshift galaxies in the rest-frame UV wavelength range and to study the evolution of the cosmic star-formation density at z~7. The GOODS-South area was surveyed down to a limiting magnitude of about (J+Ks)=25.5 looking for drop-out objects in the z ACS filter. The large sampled area would allow for the detection of galaxies which are 20 times less numerous and 1-2 magnitudes brighter than similar studies using HST/NICMOS near-IR data. Two objects were initially selected as promising candidates of galaxies at z~7, but have subsequently been dismissed and identified as Galactic brown dwarfs through a detailed analysis of their morphology and Spitzer colors, as well as through spectroscopic information. As a consequence, we conclude that there are no galaxies at z~7 down to our limiting magnitude in the field we investigated. Our non detection of galaxies at z~7 provides clear evidence for a strong evolution of the luminosity function between z=6 and z=7, i.e. over a time interval of only ~170 Myr. Our constraints also provide evidence for a significant decline of the total star formation rate at z=7, which must be less than 40% of that at z=3 and 40-80% of that at z=6. We also derive an upper limit to the ionizing flux at z=7, which is only marginally consistent with that required to completely ionize the Universe.

astro-ph↗

arXiv2006

The Kormendy relation of massive elliptical galaxies at z~1.5. Evidence for size evolution ?

We present the morphological analysis based on HST-NIC2 (0.075 arcsec/pixel) images in the F160W filter of a sample of 9 massive field (> 10^{11} M_\odot) galaxies spectroscopically classified as early-types at 1.2 within R_e of our galaxies and we compared them with those of early-types at lower redshifts. We find that the surface brightness of our galaxies should get fainter by 2.5 mag from z~1.5 to z~0 to match the surface brightness of the local ellipticals with comparable R_e, i.e. the local Kormendy relation. Luminosity evolution without morphological changes can only explain half of this effect, as the maximum dimming expected for an elliptical galaxy is ~1.6 mag in this redshift range. Thus, other parameters, possibly structural, may undergo evolution and play an important role in reconciling models and observations. Hypothesizing an evolution of the effective radius of galaxies we find that R_e should increase by a factor 1.5 from z~1.5 to z~0.

astro-ph↗

arXiv2006

Extremely compact massive galaxies at z~1.4

The optical rest-frame sizes of 10 of the most massive (~5x10^{11}h_{70}^{-2}M_sun) galaxies found in the near-infrared MUNICS survey at 1.2<z<1.7 are analysed. Sizes were estimated both in the J and K' filters. These massive galaxies are at least a factor of 4_{-1.0}^{+1.9} (+-1 sigma) smaller in the rest-frame V-band than local counterparts of the same stellar mass. Consequently, the stellar mass density of these objects is (at least) 60 times larger than massive ellipticals today. Although the stellar populations of these objects are passively fading, their structural properties are rapidly changing since that redshift. This observational fact disagrees with a scenario where the more massive and passive galaxies are fully assembled at z~1.4 (i.e. a monolithic scenario) and points towards a dry merger scenario as the responsible mechanism for the subsequent evolution of these galaxies.

astro-ph↗