arXiv subjects

F. Mannucci

Publications and source records attributed to F. Mannucci.

At least 163 records · Page 9Linked to original sources

arXiv2006

Galaxy morphology and evolution from SWAN Adaptive Optics imaging

We present the results from adaptive optics (AO) assisted imaging in the Ks band of an area of 15 arcmin^2 for SWAN (Survey of a Wide Area with NACO). We derive the high resolution near-IR morphology of ~400 galaxies up to Ks~23.5 in the first 21 SWAN fields around bright guide stars, carefully taking into account the survey selection effects and using an accurate treatment of the anisoplanatic AO PSF. The detected galaxies are sorted into two morphological classes according to their Sersic index. The extracted morphological properties and number counts of the galaxies are compared with the predictions of different galaxy formation and evolution models, both for the whole galaxy population and separately for late-type and early-type galaxies. This is one of the first times such a comparison has been done in the near-IR, as AO observations and accurate PSF modeling are needed to obtain reliable morphological classification of faint field galaxies at these wavelengths. For early-type galaxies we find that a pure luminosity evolution model, without evidence for relevant number and size evolution, better reproduces the observed properties of our Ks-selected sample than current semi-analytic models based on the hierarchical picture of galaxy formation. In particular, we find that the observed flattening of elliptical galaxy counts at Ks~20 is quantitatively in good agreement with the prediction of the pure luminosity evolution model that was calculated prior to the observation. For late-type galaxies, while both models are able to reproduce the number counts, we find some hints of a possible size growth. These results demonstrate the unique power of AO observations to derive high resolution details of faint galaxies' morphology in the near-IR and drive studies of galaxy evolution.

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arXiv2006

A new formulation of the Type Ia SN rate and its consequences on galactic chemical evolution

In recent papers Mannucci et al. (2005, 2006) suggested, on the basis of observational arguments, that there is a bimodal distribution of delay times for the explosion of Type Ia SNe. In this paper, we test this hypothesis in models of chemical evolution of galaxies of different morphological type: ellipticals, spirals and irregulars. We show that this proposed scenario is compatible also with the main chemical properties of galaxies. When the new rate is introduced in the two-infall model for the Milky Way, the derived Type Ia SN rate as a function of cosmic time shows a high and broad peak at very early epochs thus influencing the chemical evolution of the galactic halo more than in the previous widely adopted formulations for the SNIa rate. As a consequence of this, the [O/Fe] ratio decreases faster for [Fe/H] > -2.0 dex, relative to the old models. For a typical elliptical of 10^11 M_sun of luminous mass, the new rate produces average [alpha/ Fe] ratios in the dominant stellar population still in agreement with observations. The Type Ia SN rate also in this case shows an earlier peak and a subsequent faster decline relative to the previous results, but the differences are smaller than in the case of our Galaxy. We have also checked the effects of the new Type Ia SN rate on the evolution of the Fe content in the ICM, as a consequence of its production from cluster ellipticals and we found that less Fe in the ICM is produced with the new rate, due to the higher fraction of Fe synthesized at early times and remaining locked into the stars in ellipticals. For dwarf irregular galaxies suffering few bursts of star formation we obtain [O/Fe] ratios larger by 0.2 dex relative to the previous models.

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arXiv2006

Two populations of progenitors for type Ia SNe?

We use recent observations of type Ia Supernova (SN Ia) rates to derive, on robust empirical grounds, the distribution of the delay time (DTD) between the formation of the progenitor star and its explosion as a SN. Our analysis finds: i) delay times as long as 3-4 Gyr, derived from observations of SNe Ia at high redshift, cannot reproduce the dependence of the SN Ia rate on the colors and on the radio-luminosity of the parent galaxies, as observed in the local Universe; ii) the comparison between observed SN rates and a grid of theoretical "single-population" DTDs shows that only a few of them are possibly consistent with observations. The most successful models are all predicting a peak of SN explosions soon after star formation and an extended tail in the DTD, and can reproduce the data but only at a modest statistical confidence level; iii) present data are best matched by a bimodal DTD, in which about 50% of type Ia SNe (dubbed "prompt" SN Ia) explode soon after their stellar birth, in a time of the order of 10^8 years, while the remaining 50% ("tardy" SN Ia) have a much wider distribution, well described by an exponential function with a decay time of about 3 Gyr. This fact, coupled with the well established bimodal distribution of the decay rate, suggests the existence of two classes of progenitors. We discuss the cosmological implications of this result and make simple predictions. [Abridged]

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arXiv2005

GRB 021004 modelled by multiple energy injections

GRB 021004 is one of the best sampled gamma-ray bursts (GRB) to date, although the nature of its light curve is still being debated. Here we present a large amount (107) of new optical, near-infrared (NIR) and millimetre observations, ranging from 2 hours to more than a year after the burst. Fitting the multiband data to a model based on multiple energy injections suggests that at least 7 refreshed shocks took place during the evolution of the afterglow, implying a total energy release (collimated within an angle of 1.8 deg) of ~ 8x10^51 erg. Analysis of the late photometry reveals that the GRB 021004 host is a low extinction (Av ~ 0.1) starburst galaxy with M_B ~ -22.0.

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arXiv2005

Dating the stellar population in massive early-type galaxies at $z\sim$1.5

We present the analysis of 10 massive early-type galaxies at $z\sim1.5$. They have been identified by means of a near-IR low resolution spectroscopic follow-up of a complete sample of 36 bright (K' $<$ 18.5) Extremely Red Objects (EROs, R-K'$>$ 5) selected from the Munich Near-IR ClusterSurvey (MUNICS; Drory et al. 2001). The low resolution near-IR spectra constrain their redshift at $1.2 2$ for all the galaxies and $z_{f} \geq 4$ for the oldest ones. The comparison of the 4000Åbreak and of the overall spectral shape of the average spectrum of the 10 galaxies at $z\sim1.5$ with those of their local counterpartsconfirms that field massive early-type galaxies formed the bulk of their stellar mass at $2<z<4$, most likely over a short ($<$ 1 Gyr) star formation time scale, consistently with the results derived from the analysis of their individual spectro-photometric properties.

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arXiv2005

Why Are Radio-Galaxies Prolific Producers of Type Ia Supernovae?

An analysis of SNIa events in early type galaxies from the Cappellaro et al (1999) database provides conclusive evidence that the rate of type Ia Supernovae (SNe) in radio-loud galaxies is about 4 times higher than the rate measured in radio-quiet galaxies, i.e. SNIa-rate$(radio-loud galaxies) = 0.43^{+0.19}_{-0.14}h^2_{75}$ SNu as compared to SNIa-rate$(radio-quiet galaxies) = 0.11^{+0.06}_{-0.03}h^2_{75}$ SNu. The actual value of the enhancement is likely to be in the range $\sim 2-7$ (P$\sim 10^{-4}$). This finding puts on robust empirical grounds the results obtained by Della Valle & Panagia (2003) on the basis of a smaller sample of SNe. We analyse the possible causes of this result and conclude that the enhancement of SNIa explosion rate in radio-loud galaxies has the same origin as their being strong radio sources, but there is no causality link between the two phenomena. We argue that repeated episodes of interaction and/or mergers of early type galaxies with dwarf companions, on times-scale of about 1 Gyr, are responsible for inducing both strong radio activity observed in $\sim$14% of early type galaxies and to supply an adequate number of SNIa progenitors to the stellar population of ellipticals.

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arXiv2005

Constraining the thermal history of the Warm-Hot Intergalactic Medium

We have identified a large-scale structure traced by galaxies at z=0.8, within the Lockman Hole, by means of multi-object spectroscopic observations. By using deep XMM images we have investigated the soft X-ray emission from the Warm-Hot Intergalactic Medium (WHIM) expected to be associated with this large-scale structure and we set a tight upper limit to its flux in the very soft 0.2-0.4 keV band. The non-detection requires the WHIM at these redshifts to be cooler than 0.1 keV. Combined with the WHIM emission detections at lower redshift, our result indicates that the WHIM temperature is rapidly decreasing with redshift, as expected in popular cosmological models.

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arXiv2004

Warm-Hot Intergalactic Medium in the Sculptor Supercluster

We have analyzed the soft X-ray emission in a wide area of the Sculptor supercluster by using overlapping ROSAT PSPC pointings. After subtraction of the point sources we have found evidence for extended, diffuse soft X-ray emission. We have investigated the nature of such extended emission through the cross-correlation with the density of galaxies as inferred from the Muenster Redshift Survey. In particular we have analyzed the correlation as a function of the temperature of the X-ray emitting gas. We have found a significant correlation of the galaxy distribution only with the softest X-ray emission (0.1--0.3 keV) and only for gas temperatures kT < 0.5 keV. We have excluded that this soft X-ray diffuse emission, and its correlation with the galaxy distribution, is significantly contributed by unresolved AGN, group of galaxies or individual galaxies. The most likely explanation is that the soft, diffuse X-ray emission is tracing Warm-Hot Intergalactic Medium, with temperatures below 0.5 keV, associated with the large-scale structures in the Sculptor supercluster.

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arXiv2004

The density of very massive evolved galaxies to z~1.7

We spectroscopically identified 7 massive evolved galaxies with magnitudes 17.8 ~1.5, a factor 1.5 lower than the density (8.4(+-1) x 10^{-5} Mpc^{-3}) of early-types with comparable masses at z=0. The incompleteness (30%) of our spectroscopic observations accounts for this discrepancy. Thus, our data do not support a decrease of the comoving density of early-type galaxies with masses comparable to the most massive ones in the local Universe up to z~1.7. This suggests that massive evolved galaxies do not play an important role in the evolution of the mass density outlined by recent surveys in this redshift range, evolution which instead has to be ascribed to the accretion of the stellar mass in late-type galaxies. Finally, the presence of such massive evolved galaxies at these redshifts suggests that the assembly of massive spheroids has taken place at z>2 supporting a high efficiency in the accretion of the stellar mass in massive halos in the early Universe.

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arXiv2004

The supernova rate per unit mass

We compute the rate of supernovae (SNe) of different types along the Hubble sequence normalized to the near-infrared luminosity and to the stellar mass of the parent galaxies. This is made possible by the new complete catalog of near-infrared galaxy magnitudes obtained by 2MASS. We find that the rates of all SN types, including Ia, Ib/c and II, show a sharp dependence on both the morphology and the (B-K) colors of the parent galaxies and, therefore, on the star formation activity. In particular we find, with a high statistical significance, that the type Ia rate in late type galaxies is a factor ~20 higher than in E/S0. Similarly, the type Ia rate in the galaxies bluer than B-K=2.6 is about a factor of 30 larger than in galaxies with B--K>4.1. These findings can be explained by assuming that a significant fraction of Ia events in late Spirals/Irregulars originates in a relatively young stellar component.

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arXiv2004

Looking for obscured QSOs in the X-ray emitting ERO population

We present XMM-Newton data centered on one of the MUNICS Near Infrared Cluster Survey fields (S2F1) and we discuss the X-ray properties of the 6 X-ray emitting EROs found. For one of them we have already obtained the redshift using near-infrared spectroscopic data, while for the remaining 5 EROs the analysis is based on photometric redshifts. We find evidence for the presence of an X-ray obscured QSO in at least 5 out of the 6 X-ray emitting EROs. For these 5 objects we derive intrinsic (2-10 keV) luminosities in excess of 10^44 erg/s and intrinsic column densities higher than 10^22 cm^-2. These values have been obtained through a basic X-ray spectral analysis for the three brightest sources and through the analysis of the hardness ratios for the remaining two. All of these 5 X-ray emitting EROs appear extended in the optical/near-infrared bands indicating that the host galaxy emission dominates at these wavelengths. This suggests that the hosted AGNs are likely to be absorbed also in the optical/near-infrared bands: i.e. they are likely X-ray obscured possible type 2 QSOs. For the remaining ERO the presence of an AGN is suggested both by its high 0.5-2 keV luminosity (L(0.5-2 keV)~10^43 erg/s) and by its X-ray-to-optical flux ratio. In this case the quality of the present data prevents us from placing firm constraints on the AGN type hosted. Finally, the near-IR spectrum obtained for one of the 6 EROs classifies the host galaxy as an elliptical at z~1.7 with a stellar mass well in excess of 10^11 M_\odot. This result corroborates the possible link between the QSO activity and the formation of massive spheroids.

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arXiv2004

A supernova origin for dust in a high-redshift quasar

Interstellar dust plays a crucial role in the evolution of the Universe by assisting the formation of molecules, by triggering the formation of the first low-mass stars, and by absorbing stellar ultraviolet-optical light and subsequently re-emitting it at infrared/millimetre wavelengths. Dust is thought to be produced predominantly in the envelopes of evolved (age >1 Gyr), low-mass stars. This picture has, however, recently been brought into question by the discovery of large masses of dust in the host galaxies of quasars at redshift z>6, when the age of the Universe was less than 1 Gyr. Theoretical studies, corroborated by observations of nearby supernova remnants, have suggested that supernovae provide a fast and efficient dust formation environment in the early Universe. Here we report infrared observations of a quasar at redshift 6.2, which are used to obtain directly its dust extinction curve. We then show that such a curve is in excellent agreement with supernova dust models. This result demonstrates a supernova origin for dust in this high-redshift quasar, from which we infer that most of the dust at high redshifts has probably the same origin.

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arXiv2004

Probing a GRB progenitor at a redshift of z=2: a comprehensive observing campaign of the afterglow of GRB 030226

We report results from a comprehensive follow-up observing campaign of the afterglow of GRB 030226, including VLT spectroscopy, VLT polarimetry, and Chandra X-ray observations. In addition, we present BOOTES-1 wide-field observations at the time of the occurrence of the burst. First observations at ESO started 0.2 days after the event when the GRB afterglow was at a magnitude of R~19 and continued until the afterglow had faded below the detection threshold (R>26). No underlying host galaxy was found. The optical light curve shows a break around 0.8 days after the burst, which is achromatic within the observational errors, supporting the view that it was due to a jetted explosion. Close to the break time the degree of linear polarization of the afterglow light was less than 1.1%, which favors a uniform jet model rather than a structured one. VLT spectra show two absorption line systems at redshifts z=1.962+/-0.001 and at z=1.986+/-0.001, placing the lower limit for the redshift of the GRB close to 2. We emphasize that the kinematics and the composition of the absorbing clouds responsible for these line systems is very similar to those observed in the afterglow of GRB 021004. This corroborates the picture in which at least some GRBs are physically related to the explosion of a Wolf-Rayet star.

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arXiv2004

Nuclear star formation in the quasar PG1126-041 from adaptive optics assisted spectroscopy

We present adaptive optics assisted spectroscopy of three quasars obtained with NACO at VLT. The high angular resolution achieved with the adaptive optics (~0.08"), joined to the diagnostic power of near-IR spectroscopy, allow us to investigate the properties of the innermost 100 pc of these quasars. In the quasar with the best adaptive optics correction, PG1126-041, we spatially resolve the Pa-alpha emission within the nuclear 100 pc. The comparison with higher excitation lines suggests that the narrow Pa-alpha emission is due to nuclear star formation. The inferred intensity of the nuclear star formation (13 M(sun)/yr) may account for most of the far-IR luminosity observed in this quasar.

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arXiv2004

Extreme gas properties in the most distant quasars

We present near-IR, low resolution spectra of eight of the most distant quasars known, with redshifts in the range 4.9<z<6.4. Half of these quasars are characterized by deep, broad and blueshifted absorption features associated with both high and low ionization species (CIV, SiIV, AlIII, MgII), i.e. they belong to the class of Broad Absorption Line (BAL) quasars, which are associated with powerful outflows of dense gas. Although the sample is small, the large fraction of BAL quasars, the depth and ionization state of the absorption features suggest that these most distant quasars are surrounded by a much larger amount of dense gas than lower redshift (z<4) quasars. The possible interpretation in terms of extremely high accretion rates and the association with the early formation of quasars and of their host galaxies is discussed. The absorption properties of the dust, associated with the gas along the line of sight, appear different with respect to lower redshift quasars, possibly indicating different dust physics at these highest redshifts.

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arXiv2004

Detections of Warm-Hot Intergalactic Medium

Several popular cosmological models predict that most of the baryonic mass in the local universe is located in filamentary and sheet-like structures associated with groups and clusters of galaxies. This gas is expected to be gravitationally heated to ~10^6 K and therefore emitting in the soft X-rays. We have investigated three fields with large scale structures of galaxies at redshifts 0.1, 0.45, 0.79 and found signatures of warm-hot thermal emission (kT< 1 keV) correlated with the distribution of galaxies for the first two. The correlation and the properties of both X-ray and galaxy distribution strongly suggest that the diffuse X-ray flux is due to extragalactic emission by the Warm-Hot Intergalactic Medium (WHIM) predicted by cosmological models.

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arXiv2003

The TESIS project: revealing massive early-type galaxies at z>1

We present the preliminary results of an on-going near-IR low resolution spectroscopic follow-up of a complete sample of 30 bright (K'<18.5) EROs selected over 360 arcmin^2 from the MUNICH survey. Among the 13 EROs observed so far, 7 turned out to be early-type galaxies at 1.2 1.

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arXiv2003

The TESIS project: Are type 2 QSO hidden in X-ray emitting EROs?

Here we present the results obtained from the analysis of 75 ksec of XMM-Newton observations of a sample of EROs selected from one MUNICS field (K'<19.5 mag). We find 6 EROs with a X-ray counterpart down to a 2--10 keV flux limit of ~10^{-15} cgs. For all of them the X-ray--to--optical flux ratios and the 2--10 keV luminosities suggest the presence of AGN. In particular, a complete X-ray spectral analysis shows that high luminosity, obscured AGNs (i.e. QSO2 candidates) are present in 3 of them.

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