arXiv subjects

L. Morselli

Publications and source records attributed to L. Morselli.

25 records · Page 2Linked to original sources

arXiv2018

HDUV: The Hubble Deep UV Legacy Survey

We present the Hubble Deep UV Legacy Survey (HDUV), a 132 orbit imaging program with the WFC3/UVIS camera onboard the Hubble Space Telescope (HST). The HDUV extends and builds on the few previous UV imaging surveys in the two GOODS/CANDELS-Deep fields to provide deep images over a total area of ~100 arcmin2 in the two filters F275W and F336W. Our release also includes all the F275W imaging data taken by the CANDELS survey, which were aligned using a novel approach and combined with the HDUV survey data. By reaching depths of 27.5-28.0 mag (5sigma, in 0.4" apertures), these are the deepest high-resolution UV data over such a large area taken to date. Such unique UV imaging enables a wide range of science by the community. Among the main goals of the HDUV survey are: (1) provide a complete sample of faint star-forming galaxies at z~1-3, (2) constrain the ionizing photon escape fraction from galaxies at z~2-3, and (3) track the build-up of bulges and the disappearance of clumpy disk galaxies through reliable internal stellar population properties at sub-kpc resolution out to z~3. The addition of the HDUV data further enhances the legacy value of the two GOODS/CANDELS-Deep fields, which now include deep 11-band HST imaging as well as very deep ancillary data from X-ray to radio, enabling unique multi-wavelength studies. Here, we provide an overview of the survey design, describe the data reduction, and highlight a few basic analyses on the images which are released to the community as high level science products via the Mikulski Archive for Space Telescopes (MAST).

astro-ph.GA↗

arXiv2017

Light breeze in the local Universe

We analyze a complete spectroscopic sample of galaxies ($\sim$600,000 ) drawn from Sloan Digital Sky Survey (SDSS, DR7) to look for evidence of galactic winds in the local Universe. We focus on the shape of the [OIII]$λ$5007 emission line as a tracer of ionizing gas outflows. We stack our spectra in a fine grid of star formation rate (SFR) and stellar mass to analyze the dependence of winds on the position of galaxies in the SFR versus mass diagram. We do not find any significant evidence of broad and shifted [OIII]$λ$5007 emission line which we interpret as no evidence of outflowing ionized gas in the global population. We have also classified these galaxies as star-forming or AGN dominated according to their position in the standard BPT diagram. We show how the average [OIII]$λ$5007 profile changes as function of nature of the dominant ionizing source. We find that in the star-forming dominated source the oxygen line is symmetric and governed by the gravitational potential well. The AGN or composite AGN$\setminus$star-formation activity objects, in contrast, display a prominent and asymmetric profile that can be well described by a broad gaussian component that is blue-shifted from a narrow symmetric core. In particular, we find that the blue wings of the average [OIII]$λ$5007 profiles are increasingly prominent in the LINERs and Seyfert galaxies. We conclude that, in the low-redshift Universe, "pure" star-formation activity does not seem capable of driving ionized-gas outflows, while, the presence of optically selected AGN seems to play a primary role to drive such winds. We discuss the implications of these results for the role of the quenching mechanism in the present day Universe.

astro-ph.GA↗

arXiv2016

The HDUV Survey: Six Lyman Continuum Emitter Candidates at z~2 Revealed by HST UV Imaging

We present six galaxies at z~2 that show evidence of Lyman continuum (LyC) emission based on the newly acquired UV imaging of the Hubble Deep UV legacy survey (HDUV) conducted with the WFC3/UVIS camera on the Hubble Space Telescope (HST). At the redshift of these sources, the HDUV F275W images partially probe the ionizing continuum. By exploiting the HST multi-wavelength data available in the HDUV/GOODS fields, models of the UV spectral energy distributions, and detailed Monte Carlo simulations of the intergalactic medium absorption, we estimate the absolute ionizing photon escape fractions of these galaxies to be very high -- typically >60% (>13% for all sources at 90% likelihood). Our findings are in broad agreement with previous studies that found only a small fraction of galaxies to show high escape fraction. These six galaxies comprise the largest sample yet of LyC leaking candidates at z~2 whose inferred LyC flux has been cleanly observed at HST resolution. While three of our six candidates show evidence of hosting an active galactic nucleus (AGN), two of these are heavily obscured and their LyC emission appears to originate from star-forming regions rather than the central nucleus. This suggests an AGN-aided pathway for LyC escape from these sources. Extensive multi-wavelength data in the GOODS fields, especially the near-IR grism spectra from the 3D-HST survey, enable us to study the candidates in detail and tentatively test some recently proposed indirect methods to probe LyC leakage -- namely, the [OIII]/[OII] line ratio and the H$β-$UV slope diagram. High-resolution spectroscopic followup of our candidates will help constrain such indirect methods which are our only hope of studying $f_{esc}$ at z~5-9 in the fast-approaching era of the James Webb Space Telescope.

astro-ph.GA↗

arXiv2016

Bulges and disks in the local Universe. Linking the galaxy structure to star formation activity

We use a sample built on the SDSS DR7 catalogue and the bulge-disc decomposition of Simard et al. (2011) to study how the bulge and disc components contribute to the parent galaxy's star formation activity, by determining its position in the star formation rate (SFR) - stellar mass (M$_{\star}$) plane at 0.02$<z<$0.1. We use the bulge and disc colours as proxy for their SFRs. We study the mean galaxy bulge-total mass ratio (B/T) as a function of the residual from the MS ($Δ_{MS}$) and find that the B/T-$Δ_{MS}$ relation exhibits a parabola-like shape with the peak of the MS corresponding to the lowest B/Ts at any stellar mass. The lower and upper envelop of the MS are populated by galaxies with similar B/T, velocity dispersion and concentration ($R_{90}/R_{50}$) values. Bulges above the MS are characterised by blue colours or, when red, by a high level of dust obscuration, thus indicating that in both cases they are actively star forming. When on the MS or below it, bulges are mostly red and dead. At stellar masses above $10^{10.5} $M$_{\odot}$, bulges on the MS or in the green valley tend to be significantly redder than their counterparts in the quiescence region, despite similar levels of dust obscuration. The disc color anti-correlates at any mass with the distance from the MS, getting redder when approaching the MS lower envelope and the quiescence region. We conclude that the position of a galaxy in the LogSFR-LogM$_{\star}$ plane depends on the star formation activity of its components: above the MS both bulge and disk are actively star forming. The nuclear activity is the first to be suppressed, moving the galaxies on the MS. Once the disk stops forming stars as well, the galaxy moves below the MS and eventually to the quiescence region. This is confirmed by a large fraction ($\sim45\%$) of passive galaxies with a secure two component morphology.

astro-ph.GA↗

arXiv2016

The effect of disk inclination on the Main Sequence of star forming galaxies

We use the Sloan Digital Sky Survey (SDSS) database to explore the effect of the disk inclination angle on the derived star formation rate (SFR), hence on the slope and width of the Main Sequence (MS) relation for star-forming galaxies. We find that SFRs for nearly edge-on disks are underestimated by factors ranging from $\sim$ 0.2 dex for low mass galaxies up to $\sim$ 0.4 dex for high mass galaxies. This results in a substantially flatter MS relation for high-inclination disks compared to that for less inclined ones, though the global effect over the whole sample of star-forming galaxies is relatively minor, given the small fraction of high-inclination disks. However, we also find that galaxies with high-inclination disks represent a non negligible fraction of galaxies populating the so-called green valley, with derived SFRs intermediate between the MS and those of quenched, passively evolving galaxies.

astro-ph.GA↗

arXiv2015

Non-linearity and environmental dependence of the star forming galaxies Main Sequence

Using data from four deep fields (COSMOS, AEGIS, ECDFS, and CDFN), we study the correlation between the position of galaxies in the star formation rate (SFR) versus stellar mass plane and local environment at $z<1.1$. To accurately estimate the galaxy SFR, we use the deepest available Spitzer/MIPS 24 and Herschel/PACS datasets. We distinguish group environments ( $M_{halo}\sim$10$^{12.5-14.2}$$M_{\odot}$) based on the available deep X-ray data and lower halo mass environments based on the local galaxy density. We confirm that the Main Sequence (MS) of star forming galaxies is not a linear relation and there is a flattening towards higher stellar masses ( $M_*>10^{10.4-10.6}$ $M_{\odot}$), across all environments. At high redshift ( $0.5<z<1.1$ ), the MS varies little with environment. At low redshift ( $0.15<z<0.5$ ), group galaxies tend to deviate from the mean MS towards the region of quiescence with respect to isolated galaxies and less-dense environments. We find that the flattening of the MS toward low SFR is due to an increased fraction of bulge dominated galaxies at high masses. Instead, the deviation of group galaxies from the MS at low redshift is caused by a large fraction of red disk dominated galaxies which are not present in the lower density environments. Our results suggest that above a mass threshold ( $\sim10^{10.4}-10^{10.6}$$M_{\odot}$ ) stellar mass, morphology and environment act together in driving the evolution of the SF activity towards lower level. The presence of a dominating bulge and the associated quenching processes are already in place beyond $z\sim$1. The environmental effects appear, instead, at lower redshifts and have a long time-scale.

astro-ph.GA↗

arXiv2014

The primordial environment of super massive black holes: large scale galaxy overdensities around $z\sim6$ QSOs with LBT

We investigated the presence of galaxy overdensities around four $z\sim6$ QSOs, namely SDSS J1030+0524 (z = 6.28), SDSS J1148+5251 (z = 6.41), SDSS J1048+4637 (z = 6.20) and SDSS J1411+1217 (z = 5.95), through deep $r$-, $i$- and $z$- band imaging obtained with the wide-field ($\sim23'\times25'$) Large Binocular Camera (LBC) at the Large Binocular Telescope (LBT). We adopted color-color selections within the $i-z$ vs $r-z$ plane to identify samples of $i$-band dropouts at the QSO redshift and measure their relative abundance and spatial distribution in the four LBC fields, each covering $\sim8\times8$ physical Mpc at $z\sim6$. The same selection criteria were then applied to $z$-band selected sources in the $\sim$1 deg$^2$ Subaru-XMM Newton Deep Survey to derive the expected number of dropouts over a blank LBC-sized field ($\sim$0.14 deg$^2$). The four observed QSO fields host a number of candidates larger than what is expected in a blank field. By defining as $i$-band dropouts objects with $z_{AB}<25$, $i-z>1.4$ and undetected in the $r$-band, we found 16, 10, 9, 12 dropouts in SDSS J1030+0524, SDSS J1148+5251, SDSS J1048+4637, and SDSS J1411+1217, respectively, whereas only 4.3 such objects are expected over a 0.14 deg$^2$ blank field. This corresponds to overdensity significances of 3.3, 1.9, 1.7, 2.5$σ$, respectively. By considering the total number of dropouts in the four LBC fields and comparing it with what is expected in four blank fields of 0.14 deg$^2$ each, we find that high-z QSOs reside in overdense environments at the $3.7σ$ level. This is the first direct and unambiguous measurement of the large scale structures around $z\sim6$ QSOs. [shortened]

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