25 research outputs found
Using ALMA to resolve the nature of the early star-forming large-scale structure PLCK G073.4-57.5
Galaxy clusters at high redshift are key targets for understanding matter
assembly in the early Universe, yet they are challenging to locate. A sample of
>2000 high-z candidate structures has been found using Planck's all-sky submm
maps, and a sub-set of 234 have been followed up with Herschel-SPIRE, which
showed that the emission can be attributed to large overdensities of dusty
star-forming galaxies. In order to resolve and characterise the individual
galaxies we targeted the eight brightest SPIRE sources in the centre of the
Planck peak PLCK G073.4-57.5 using ALMA at 1.3 mm, and complemented these
observations with data from IRAC, WIRCam J,K, and SCUBA-2. We detected a total
of 18 millimetre galaxies brighter than 0.3 mJy in 2.4 arcmin^2. The ALMA
source density is 8-30 times higher than average background estimates and
larger than seen in typical 'proto-cluster' fields. We were able to match all
but one of the ALMA sources to a NIR counterpart. The most significant (four)
SCUBA-2 sources are not included in the ALMA pointings, but we find an 8sigma
stacking detection of the ALMA sources in the SCUBA-2 map at 850 um. We derive
photo-z, L_IR, SFR, stellar mass, T_dust, M_dust for all of the ALMA galaxies;
the photo-zs identify two groups each of five sources, at z~1.5 and 2.4. The
two groups show two 'red sequences' (i.e. similar NIR [3.6]-[4.5] colours and
different J-K colours). The majority of the ALMA-detected galaxies are on the
SFR versus stellar mass main sequence, and half of the sample is more massive
than the characteristic stellar mass at the corresponding redshift.
Serendipitous CO line detections in two of the galaxies appear to match their
photometric redshifts at z~1.54. We performed an analysis of star-formation
efficiencies and CO- and mm-continuum-derived gas fractions of our ALMA
sources, combined with a sample of 1<z<3 cluster and proto-cluster members.Comment: 26 pages, revised version, Astronomy & Astrophysics accepte
MAMBO 1.2mm observations of luminous starbursts at z~2 in the SWIRE fields
We report on--off pointed MAMBO observations at 1.2 mm of 61 Spitzer-selected
star-forming galaxies from the SWIRE survey. The sources are selected on the
basis of bright 24um fluxes (f_24um>0.4mJy) and of stellar dominated
near-infrared spectral energy distributions in order to favor z~2 starburst
galaxies. The average 1.2mm flux for the whole sample is 1.5+/-0.2 mJy. Our
analysis focuses on 29 sources in the Lockman Hole field where the average
1.2mm flux (1.9+/-0.3 mJy) is higher than in other fields (1.1+/-0.2 mJy). The
analysis of the sources multi-wavelength spectral energy distributions
indicates that they are starburst galaxies with far-infrared luminosities
~10^12-10^13.3 Lsun, and stellar masses of ~0.2-6 x10^11 M_sun. Compared to
sub-millimeter selected galaxies (SMGs), the SWIRE-MAMBO sources are among
those with the largest 24um/millimeter flux ratios. The origin of such large
ratios is investigated by comparing the average mid-infrared spectra and the
stacked far-infrared spectral energy distributions of the SWIRE-MAMBO sources
and of SMGs. The mid-infrared spectra exhibit strong PAH features, and a warm
dust continuum. The warm dust continuum contributes to ~34% of the mid-infrared
emission, and is likely associated with an AGN component. This constribution is
consistent with what is found in SMGs. The large 24um/1.2mm flux ratios are
thus not due to AGN emission, but rather to enhanced PAH emission compared to
SMGs. The analysis of the stacked far-infrared fluxes yields warmer dust
temperatures than typically observed in SMGs. Our selection favors warm
ultra-luminous infrared sources at high-z, a class of objects that is rarely
found in SMG samples. Our sample is the largest Spitzer-selected sample
detected at millimeter wavelengths currently available.Comment: Accepted for publication in ApJ (51 pages; 16 figures). The quality
of some figures has been degraded for arXiv purposes. Full resolution version
available at this
http://www.iasf-milano.inaf.it/~polletta/mambo_swire/lonsdale08_ApJ_accepted.pd
Parametric modelling of the 3.6um to 8um colour distributions of galaxies in the SWIRE Survey
We fit a parametric model comprising a mixture of multi-dimensional Gaussian
functions to the 3.6 to 8um colour and optical photo-z distribution of galaxy
populations in the ELAIS-N1 and Lockman Fields of SWIRE. For 16,698 sources in
ELAIS-N1 we find our data are best modelled (in the sense of the Bayesian
Information Criterion) by the sum of four Gaussian distributions or modes (C_a,
C_b, C_c and C_d). We compare the fit of our empirical model with predictions
from existing semi-analytic and phenomological models. We infer that our
empirical model provides a better description of the mid-infrared colour
distribution of the SWIRE survey than these existing models. This colour
distribution test is thus a powerful model discriminator and complementary to
comparisons of number counts. We use our model to provide a galaxy
classification scheme and explore the nature of the galaxies in the different
modes of the model. C_a consists of dusty star-forming systems such as ULIRG's.
Low redshift late-type spirals are found in C_b, where PAH emission dominates
at 8um. C_c consists of dusty starburst systems at intermediate redshifts. Low
redshift early-type spirals and ellipticals dominate C_d. We thus find a
greater variety of galaxy types than one can with optical photometry alone.
Finally we develop a new technique to identify unusual objects, and find a
selection of outliers with very red IRAC colours. These objects are not
detected in the optical, but have very strong detections in the mid-infrared.
These sources are modelled as dust-enshrouded, strongly obscured AGN, where the
high mid-infrared emission may either be attributed to dust heated by the AGN
or substantial star-formation. These sources have z_ph ~ 2-4, making them
incredibly infrared luminous, with a L_IR ~ 10^(12.6-14.1) L_sun.Comment: 44 pages, 10 figures, 6 tables. Accepted for publication in the
Astronomical Journa
High-Redshift QSOs in the SWIRE Survey and the z~3 QSO Luminosity Function
We use a simple optical/infrared (IR) photometric selection of high-redshift
QSOs that identifies a Lyman Break in the optical photometry and requires a red
IR color to distinguish QSOs from common interlopers. The search yields 100 z~3
(U-dropout) QSO candidates with 19<r'<22 over 11.7 deg^2 in the ELAIS-N1 (EN1)
and ELAIS-N2 (EN2) fields of the Spitzer Wide-area Infrared Extragalactic
(SWIRE) Legacy Survey. The z~3 selection is reliable, with spectroscopic
follow-up of 10 candidates confirming they are all QSOs at 2.83<z<3.44. We find
that our z~4$ (g'-dropout) sample suffers from both unreliability and
incompleteness but present 7 previously unidentified QSOs at 3.50<z<3.89.
Detailed simulations show our z~3 completeness to be ~80-90% from 3.0<z<3.5,
significantly better than the ~30-80% completeness of the SDSS at these
redshifts. The resulting luminosity function extends two magnitudes fainter
than SDSS and has a faint end slope of beta=-1.42 +- 0.15, consistent with
values measured at lower redshift. Therefore, we see no evidence for evolution
of the faint end slope of the QSO luminosity function. Including the SDSS QSO
sample, we have now directly measured the space density of QSOs responsible for
~70% of the QSO UV luminosity density at z~3. We derive a maximum rate of HI
photoionization from QSOs at z~3.2, Gamma = 4.8x10^-13 s^-1, about half of the
total rate inferred through studies of the Ly-alpha forest. Therefore,
star-forming galaxies and QSOs must contribute comparably to the
photoionization of HI in the intergalactic medium at z~3.Comment: Accepted for publication in ApJ. emulateapj format. 23 pages, 17
figure
Open Day presso lâINAF IASF di Milano Report delle prime tre edizioni (2019, 2020, 2022)
Nel 2019, lâIstituto di Astrofisica Spaziale e Fisica cosmica di Milano (IASF), una delle due sedi di Milano dellâINAF (Istituto Nazionale di Astrofisica), ha inaugurato il proprio Open Day, una giornata dedicata agli studenti universitari.
Il personale dello IASF ha aperto le porte agli studenti interessati a svolgere un progetto di ricerca presso la propria sede o, in generale, a scoprire una realtĂ professionale dedicata allo studio dellâUniverso. Gli incontri si sono divisi in due parti: nella prima sono stati presentati lâIstituto, la sua storia, le attivitĂ di ricerca in corso e le Tesi a disposizione (triennali e magistrali), mentre nella seconda si Ăš aperta una discussione libera tra i presenti durante una merenda offerta dallo IASF-Milano. Le tre edizioni svolte finora (2019, 2020 e 2022) hanno visto una buona partecipazione (circa 25-40 presenze allâanno) e hanno permesso di avvicinare ulteriormente lo IASF-Milano alle UniversitĂ del territorio, dando ai partecipanti una percezione di disponibilitĂ e accessibilitĂ della ricerca e del personale dello IASF. Dopo una pausa dovuta alla pandemia (anno 2021), lo IASF-Milano ha riaperto le porte nel 2022 in quella che ci auguriamo possa diventare una lunga tradizione
Complete Multiwavelength Characterization of Faint Chandra X-ray Sources Seen in the Spitzer Wide-Area IR Extragalactic (SWIRE) Survey
We exploit deep combined observations with Spitzer and Chandra of the SWIRE
survey in the ELAIS-N1 region, to investigate the nature of the faint X-ray and
IR sources in common, to identify AGN/starburst diagnostics, and to study the
sources of the X-ray and IR cosmic backgrounds. In the 17'x17' area of the
Chandra ACIS-I image there are 3400 SWIRE near-IR sources with 4 sigma
detections in at least 2 IRAC bands and 988 sources detected at 24micron with
MIPS brighter than 0.1 mJy. Of these, 102 IRAC and 59 MIPS sources have Chandra
counterparts, out of a total of 122 X-ray sources present in the area with
S(0.5-8 kev)>10^(-15) erg/cm^2/s. We have constructed SEDs for each source
using data from the 4 IRAC wavebands, Chandra fluxes, and optical follow-up
data in the wavebands U, g', r', i', Z, and H. We fit a number of spectral
templates to the SEDs at optical and infrared wavelengths to determine
photometric redshifts and spectral categories, and also make use of diagnostics
based on the X-ray luminosities, hardness ratios, X-ray to infrared spectral
slopes and optical morphologies. Although we have spectroscopic redshifts for
only a minority of the Chandra sources, the available SEDs constrain the
redshifts for most of the sample sources, which turn out to be typically at
0.5<z<2. We find that 39% of the Chandra sources are dominated by type-1 AGN
emission, 23% display optical/IR spectra typical of type-2 AGNs, while the
remaining 38% fraction show starburst-like or even normal galaxy spectra. Since
we prove that all these galaxies are dominated by AGN emission in X-rays this
brings the fraction of type-1 AGNs to be 80% of the type-2: even assuming that
all the Chandra sources undetected by Spitzer are type-2 AGNs, the type-1
fraction would exceed 1/3 of the total population (abridged).Comment: Accepted for publication in AJ, March 2005 issu
JWST's PEARLS: 119 multiply imaged galaxies behind MACS0416, lensing properties of caustic crossing galaxies, and the relation between halo mass and number of globular clusters at
We present a new lens model for the galaxy cluster MACS
J0416.12403 based on a previously known set of 77 spectroscopically
confirmed, multiply imaged galaxies plus an additional set of 42 candidate
multiply imaged galaxies from past HST and new JWST data. The new galaxies lack
spectroscopic redshifts but have geometric and/or photometric redshift
estimates that are presented here. The new model predicts magnifications and
time delays for all multiple images. The full set of constraints totals 343,
constituting the largest sample of multiple images lensed by a single cluster
to date. Caustic-crossing galaxies lensed by this cluster are especially
interesting. Some of these galaxies show transient events, most of which are
interpreted as micro-lensing of stars at cosmological distances. These
caustic-crossing arcs are expected to show similar events in future, deeper
JWST observations. We provide time delay and magnification models for all these
arcs. The time delays and the magnifications for different arcs are generally
anti-correlated, as expected from -body simulations.
In the major sub-halos of the cluster, the dark-matter mass from our lens
model correlates well with the observed number of globular clusters. This
confirms earlier results, derived at lower redshifts, which suggest that
globular clusters can be used as powerful mass proxies for the halo masses when
lensing constraints are scarce or not available.Comment: 21 pages and 11 figure
SWIRE: The SIRTF WideâArea Infrared Extragalactic Survey
The SIRTF Wide-Area Infrared Extragalactic Survey (SWIRE), the largest SIRTF Legacy program, is a wide-area imaging survey to trace the evolution of dusty, star-forming galaxies, evolved stellar populations, and active galactic nuclei (AGNs) as a function of environment, from redshifts to the current z ⌠3 epoch. SWIRE will survey seven high-latitude fields, totaling 60â65 deg2 in all seven SIRTF bands: Infrared Array Camera (IRAC) 3.6, 4.5, 5.6, and 8 mm and Multiband Imaging Photometer for SIRTF (MIPS) 24, 70, and 160 mm. Extensive modeling suggests that the Legacy Extragalactic Catalog may contain in excess of 2 million IR-selected galaxies, dominated by (1) âŒ150,000 luminous infrared galaxies (LIRGs; LFIR 1 1011 L,) detected by MIPS (and significantly more detected by IRAC), âŒ7000 of these with ; (2) 1 million IRAC- z 1 2 detected early-type galaxies (⌠with and âŒ10,000 with ); and (3) âŒ20,000 classical AGNs 5 2 # 10 z 1 1 z 1 2 detected with MIPS, plus significantly more dust-obscured quasi-stellar objects/AGNs among the LIRGs. SWIRE will provide an unprecedented view of the evolution of galaxies, structure, and AGNs.
The key scientific goals of SWIRE are (1) to determine the evolution of actively star forming and passively evolving galaxies in order to understand the history of galaxy formation in the context of cosmic structure formation; (2) to determine the evolution of the spatial distribution and clustering of evolved galaxies, starbursts, and AGNs in the key redshift range over which much of cosmic evolution has occurred; and (3) to 0.5 ! z ! 3 determine the evolutionary relationship between ânormal galaxiesâ and AGNs and the contribution of AGN accretion energy versus stellar nucleosynthesis to the cosmic backgrounds. The large area of SWIRE is important to establish statistically significant population samples over enough volume cells that we can resolve the star formation history as a function of epoch and environment, i.e., in the context of structure formation. The large volume is also optimized for finding rare objects.
The SWIRE fields are likely to become the next generation of large âcosmic windowsâ into the extragalactic sky. They have been uniquely selected to minimize Galactic cirrus emission over large scales. The Galaxy Evolution Explorer will observe them as part of its deep 100 deg2 survey, as will Herschel. SWIRE includes âŒ9 deg2 of the unique large-area XMM Large Scale Structure hard X-ray imaging survey and is partly covered by the UKIDSS deep J and K survey. An extensive optical/near-IR imaging program is underway from the ground. The SWIRE data are nonproprietary; catalogs and images will be released twice yearly, beginning about 11 months after SIRTF launch. Details of the data products and release schedule are presented
Chandra and Spitzer unveil heavily obscured quasars in the SWIRE/Chandra Survey
Using the large multi-wavelength data set in the chandra/SWIRE Survey (0.6
square degrees in the Lockman Hole), we show evidence for the existence of
highly obscured (Compton-thick) AGN, estimate a lower limit to their surface
density and characterize their multi-wavelength properties. Two independent
selection methods based on the X-ray and infrared spectral properties are
presented. The two selected samples contain 1) 5 X-ray sources with hard X-ray
spectra and column densities > 10^24 cm-2, and 2) 120 infrared sources with red
and AGN-dominated infrared spectral energy distributions (SEDs). We estimate a
surface density of at least 25 Compton-thick AGN per square degree detected in
the infrared in the chandra/SWIRE field of which ~40% show distinct AGN
signatures in their optical/near-infrared SEDs, the remainings being dominated
by the host-galaxy emission. Only ~33% of all Compton-thick AGN are detected in
the X-rays at our depth (F(0.3-8 keV)>10^-15 erg/cm2/s.
We report the discovery of two sources in our sample of Compton-thick AGN,
SWIRE_J104409.95+585224.8 (z=2.54) and SWIRE_J104406.30+583954.1 (z=2.43),
which are the most luminous Compton-thick AGN at high-z currently known. The
properties of these two sources are discussed in detail with an analysis of
their spectra, SEDs, luminosities and black-hole masses.Comment: ApJ accepted (to appear in May 2006 issue, vol. 642, of ApJ) Figures
2, 3, and 14 have been degraded due to space consideration