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We present the first spectroscopic confirmation of a dust-obscured dwarf galaxy, CEERS-14821. The analysis is performed combining JWST NIRCam broad-band photometry and NIRSpec/PRISM spectroscopic data. From the detection of multiple rest-frame optical lines, we derive that CEERS-14821 is located at $z=4.883\pm0.003$. Moreover, from a secure detection of the $H_{\alpha}$ and $H_{\beta}$ we derived that the galaxy has a dust extinction ranging from Av=2.2 to Av=3.3, depending on the assumed reddening law. This value is extremely large given that we estimated a low stellar mass around log(M/Mo)=8.0-8.2. Moreover, using different metallicity tracers, we verify that the galaxy is also metal-rich, with 12+log(O/H)>8.3. This is well above the expectation from both the mass-metallicity relation and the fundamental mass-metalliticy relation. CEERS-14821 is going through a burst of star formation, there are no indications of a strong contribution from an active galactic nuclei (f(AGN)<0.5 with respect to the total dust luminosity). Based on the rest-frame optical images, this source has a size compatible with galaxies of similar stellar mass and redshift. Finally, with the current data, it seems that there are galaxies closely interacting with CEERS-14821., Comment: 14 pages, 11 figures. Submitted to A&A

[abridged] We aim to constrain the stellar initial mass function (IMF) during the epoch of reionization. To this purpose, we build up a semi-empirical model for the reionization history of the Universe, based on various ingredients: the latest determination of the UV galaxy luminosity function from JWST out to redshift $z\lesssim 12$; data-inferred and simulation-driven assumptions on the redshift-dependent escape fraction of ionizing photons from primordial galaxies; a simple yet flexible parameterization of the IMF $\phi(m_\star)\sim m_\star^\xi\, e^{-m_{\star,\rm c}/m_\star}$ in terms of a high-mass end slope $\xi<0$ and of a characteristic mass $m_{\star,\rm c}$ below which a flattening or a bending sets in; the PARSEC stellar evolution code to compute the UV and ionizing emission from different star's masses as a function of age and metallicity; a few physical constraints related to stellar and galaxy formation in faint galaxies at the reionization redshifts. We compare our model outcomes with the reionization observables from different astrophysical and cosmological probes, and perform Bayesian inference on the IMF parameters. We find that the IMF slope $\xi$ is within the range from $-2.8$ to $-2.3$, while appreciably flatter slopes are excluded at great significance. However, the bestfit value of the IMF characteristic mass $m_{\star,\rm c}\sim$ a few $M_\odot$ implies a suppression in the formation of small stellar masses, at variance with the IMF in the local Universe; this may be induced by the thermal background $\sim 20-30$ K provided by CMB photons at the reionization redshifts. Finally, we investigate the implications of our reconstructed IMF on the recent JWST detections of massive galaxies at and beyond the reionization epoch, showing that any putative tension with the standard cosmological framework is substantially alleviated., Comment: 21 pages, 11 figures, typos corrected, in press on Universe

Recently we put forward a framework where the dark matter (DM) component within virialized halos is subject to a non-local interaction originated by fractional gravity (FG) effects. In previous works we demonstrated that such a framework can substantially alleviate the small-scale issues of the standard $\Lambda$CDM paradigm, without altering the DM mass profile predicted by $N-$body simulations, and retaining its successes on large cosmological scales. In this paper we dig deeper to probe FG via high-quality data of individual dwarf galaxies, by exploiting the rotation velocity profiles inferred from stellar and gas kinematic measurements in $8$ dwarf irregulars, and the projected velocity dispersion profiles inferred from the observed dynamics of stellar tracers in $7$ dwarf spheroidals and in the ultra-diffuse galaxy DragonFly 44. We find that FG can reproduce extremely well the rotation and dispersion curves of the analysed galaxies, performing in most instances significantly better than the standard Newtonian setup., Comment: 19 pages, 6 figures, accepted on Universe

We report ALMA high-resolution observations of water emission lines $p-{\rm{H_2O}} (2_{02}-1_{11}$), $o-{\rm{H_2O}} (3_{21}-3_{12})$, $p-{\rm{H_2O}} (4_{22}-4_{13})$, in the strongly lensed galaxy HATLASJ113526.2-01460 at redshift z $\sim$ 3.1. From the lensing-reconstructed maps of water emission and line profiles, we infer the general physical properties of the ISM in the molecular clouds where the lines arise. We find that the water vapor lines $o-{\rm{H_2O}} (3_{21}-3_{12})$, $p-{\rm{H_2O}} (4_{22}-4_{13})$ are mainly excited by FIR pumping from dust radiation in a warm and dense environment, with dust temperatures ranging from 70 K to $\sim 100$ K, as suggested by the line ratios. The $p-{\rm{H_2O}} (2_{02}-1_{11})$ line instead, is excited by a complex interplay between FIR pumping and collisional excitation in the dense core of the star-forming region. This scenario is also supported by the detection of the medium-level excitation of CO resulting in the line emission CO (J=8-7). Thanks to the unprecedented high resolution offered by the combination of ALMA capabilities and gravitational lensing, we discern the different phases of the ISM and locate the hot molecular clouds into a physical scale of $\sim$ 500 pc. We discuss the possibility of J1135 hosting an AGN in its accretion phase. Finally, we determine the relation between the water emission lines and the total IR luminosity of J1135, as well as the SFR as a function of water emission intensities, comparing the outcomes to local and high-$z$ galactic samples from the literature., Comment: 22 pages, 10 figures, final version to be published in Astrophysical Journal

We take advantage of the NIRCam photometric observations available as part of the Cosmic Evolution Early Release Science survey (CEERS) to identify and analyse very red sources in an effort to discover very dusty star forming galaxies. We select red galaxies as objects with a S/N>3 at 4.4 $\mu$m and a S/N<2 in all JWST and HST filters at $\lambda\leq2\mu$m, which corresponds to [F200W]-[F444W]>1.2 considering CEERS depths. This selection is ideal to identify very dusty (Av>1 mag) galaxies with stellar masses between $10^6$ to $10^{10}\, \rm M_{\odot}$ at z<5, more massive dusty galaxies at z=5-18 and galaxies at z>18 due to the Lyman absorption, independently of their dust extinction. Our sample of F200W-dropouts contains no strong candidates at z>6.5, instead it consists almost completely (~81%) of z<2 low-mass galaxies, with a median stellar mass of $10^{7.3} \rm M_{\odot}$. These galaxies show an exceptional dust extinction with median value of Av=4.9 mag, completely unexpected given their low stellar mass. The remaining galaxies, which are at z<6.5, show similar large dust extinction (Av>1), but they are generally more massive $>10^{7.5}\rm M_{\odot}$., Comment: 30 pages, 1 table, 19 figures, accepted for publication in A&A

GRB 020321 is a faint GRB that received wide follow-up attention in X-rays (BeppoSAX/NFI, Chandra/ACIS-S, XMM-Newton), radio (ATCA) and optical (ESO, HST). We identify a weak X-ray afterglow by a combined study of the Chandra and XMM-Newton observations. Its decay index of 1.2 is typical for GRB afterglows. Inside the 4"-accurate error box there is a weak optical counterpart candidate with a much shallower decay index., Comment: 5 pages, 3 figures, to be published in Proc. "GRBs in the afterglow era: 3rd Rome workshop (2002)", eds. L. Piro, F. Frontera, N. Masetti, M. Feroci

We have examined the complete set of X-ray afterglow observations of dark and optically bright GRBs performed by BeppoSAX until February 2001. X-ray afterglows are detected in 90% of the cases. We do not find significant differences in the X-ray spectral shape, in particular no higher X-ray absorption in GRBs without optical transient (dark GRBs) compared to GRBs with optical transient (OTGRBs). Rather, we find that the 1.6-10 keV flux of OTGRBs is on average about 5 times larger than that of the dark GRBs. A K-S test shows that this difference is significant at 99.8% probability. Under the assumption that dark and OTGRB have similar spectra, this could suggest that the first are uncaught in the optical band because they are just faint sources. In order to test this hypothesis, we have determined the optical-to-X ray flux ratios of the sample. OTGRBs show a remarkably narrow distribution of flux ratios, which corresponds to an average optical-to-x spectral index 0.794\pm 0.054. We find that, while 75% of dark GRBs have flux ratio upper limits still consistent with those of OT GRBs, the remaining 25% are 4 - 10 times weaker in optical than in X-rays. The significance of this result is equal to or higher than 2.6 sigma. If this sub-population of dark GRBs were constituted by objects assimilable to OTGRBs, they should have shown optical fluxes higher than upper limits actually found. We discuss the possible causes of their behaviour, including a possible occurrence in high density clouds or origin at very high redshift and a connection with ancient, Population III stars., Comment: 19 pages, 5 figures. To be published in The Astrophysical Journal

The gamma-ray burst GRB000210 had the highest gamma-ray peak flux of any event localized by BeppoSAX as yet but it did not have a detected optical afterglow. It is therefore one of the events recently classified as dark GRBs or GHOST (GRB Hiding Optical Source Transient), whose origin is still unclear. Chandra observations allowed us to localize this GRB within ~1" and a radio transient was detected with the VLA. We identify the likely (P=0.01) host galaxy of this burst at z=0.846. The X-ray spectrum of the afterglow shows intrinsic absorption N_H=5x10**21 cm-2. The amount of dust needed to absorb the optical flux of this object is consistent with the above HI column density, given a dust-to-gas ratio similar to that of our Galaxy. We do not find evidence for a partially ionized absorber expected if the absorption takes place in a Giant Molecular Cloud. We therefore conclude that either the gas is local to the GRB, but is condensed in small-scale high-density (n>~10**9 cm-3) clouds, or that the GRB is located in a dusty, gas-rich region of the galaxy. Finally, if GRB000210 lies at z>5, its X-ray absorbing medium would have to be substantially different from that observed in GRBs with optical afterglows., Comment: 29 pages, 7 fig.s, some revisions, ApJ, in press

We analyze the BeppoSAX measurements of the prompt and afterglow emission of the gamma-ray burst GRB010222. Among 45 GRBs detected with the Wide Field Cameras on BeppoSAX, the 40-700 keV fluence of (9.3+/-0.3)E-5 erg cm-2 is only surpassed by GRB990123. In terms of the isotropic 20-2000 keV energy output of 7.8E53 erg, it ranks third of all GRBs with measured distances. Since this burst is so bright, the data provide complete and valuable coverage up to 65 hr after the event, except for a gap between 3.5 and 8.0 hr. The 2-10 keV flux history shows clear signs of a break which is consistent with a break seen in the optical, and provides supporting evidence for the achromatic nature of the break. An explanation for the break in the context of a collimated expansion is not straightforward. Rather, a model is favored whereby the fireball is braked to the non-relativistic regime quickly (within a fraction of day) by a dense 1E6 cm-3 circumburst medium. This implies that, after a mild beaming correction, GRB010222 may be the most energetic burst observed thus far. The X-ray decay index after the break is 1.33+/-0.04, the spectral index 0.97+/-0.05. The decay is, with unprecedented accuracy, identical to that observed in the optical., Comment: Accepted on June 6 for publication in ApJ part I. Publication due in October 2001. Accepted version has only minor modifications

We report the discovery of a transient equivalent hydrogen column density with an absorption edge at ~3.8 kiloelectron volts in the spectrum of the prompt x-ray emission of gamma-ray burst (GRB) 990705. This feature can be satisfactorily modeled with a photoelectric absorption by a medium located at a redshift of ~0.86 and with an iron abundance of ~75 times the solar one. The transient behavior is attributed to the strong ionization produced in the circumburst medium by the GRB photons. The high iron abundance points to the existence of a burst environment enriched by a supernova along the line of sight. The supernova explosion is estimated to have occurred about 10 years before the burst. Our results agree with models in which GRBs originate from the collapse of very massive stars and are preceded by a supernova event, Comment: 15 pages,3 fig.s, link to the published paper in Science, 290, 953 (2000) through http://tonno.tesre.bo.cnr.it/~amati/curric/node6.html#papsci

GRB 991014 is one of the shortest gamma-ray bursts detected so far with the Wide Field Cameras aboard BeppoSAX, both in gamma-rays and X-rays. The duration is 9.6 sec in 2-28 keV and 3.2 sec in 40 to 700 keV (as measured between the times when 5 and 95% of the burst photons have been accumulated). We refine the InterPlanetary Network annulus of the burst, present the detection of the X-ray afterglow of GRB 991014 within this refined annulus, and discuss X-ray and gamma-ray observations of the prompt and afterglow emission. Except for the briefness of the prompt event, no other unusual aspects were found in the prompt and afterglow observations as compared to such measurements in previous gamma-ray bursts., Comment: accepted for publication in Astrophysical Journal

We present some statistical considerations on the BeppoSAX hunt for subsecond GRBs at the Scientific Operation Center. Archive analysis of a BATSE/SAX sub-sample of bursts indicates that the GRB Monitor is sensitive to short (< 2 sec) events, that are in fact about 22% of the total. The non-detection of corresponding prompt X-ray counterparts to short bursts in the Wide Field Cameras, in about 3 years of operations, is discussed: with present data no implications on the X-to-gamma-ray spectra of short vs long GRBs may be inferred. Finally, the status of searching procedures at SOC is reviewed., Comment: Proc. 5th Huntsville GRB Symposium

The results of a BeppoSAX TOO observation of the BL Lac object Mkn421 during a high intensity state are reported and compared with monitoring X-ray data collected with the BeppoSAX Wide Field Cameras (WFC) and the RXTE All Sky Monitor(ASM). The 0.1-100 keV spectrum of Mkn421 shows continuous convex curvature that can be interpreted as the high-energy end of the synchrotron emission. The source shows significant short-term temporal and spectral variability, which can be interpreted in terms of synchrotron cooling. The comparison of our results with those of previous observations when the source was a factor 3-5 fainter shows evidence for strong spectral variability, with the maximum of the synchrotron power shifting to higher energy during high states. This behaviour suggest an increase in the number of energetic electrons during high states., Comment: 6 pages, LaTeX, plus 8 .ps figures, accepted by MNRAS

Until recently the positions of gamma ray bursts were not sufficiently well known within a short timescale to localize and identify them with known celestial sources. Following the historical detection of the X-ray afterglow of the burst GRB970228, extending from 30 s to 3 days after the main peak, by the Beppo-SAX satellite and that of an optical transient 21 hr after the burst, we report here the detection of the same optical transient, in images obtained only 16 hours after the burst., Comment: Accepted for publication in Astronomy and Astrophysics Letters, Springer LateX needed