arXiv subjects

M. Negrello

Publications and source records attributed to M. Negrello.

At least 55 records · Page 3Linked to original sources

arXiv2017

Chandra and ALMA observations of the nuclear activity in two strongly lensed star forming galaxies

Nuclear activity and star formation play relevant roles in the early stages of galaxy formation. We aim at identifying them in high redshift galaxies by exploiting high-resolution and sensitivity X-ray and mm data to confirm their presence and relative role in contributing to the galaxy SEDs and energy budget. We present the data, model and analysis in the X-ray and mm bands for two strongly lensed galaxies, SDP.9 and SDP.11, selected in the Herschel-ATLAS catalogues as having an excess emission in the mid-IR regime at z>1.5, suggesting nuclear activity in the early stages of galaxy formation. We observed both of them in X-ray with Chandra and analyzed the high-resolution mm data available in the ALMA Science Archive for SDP9, and, by combining the information available, we reconstructed the source morphology. Both the targets were detected in the X-ray, strongly indicating the presence of highly obscured nuclear activity. High resolution ALMA observations for SDP9 in continuum and CO(6-5) spectral line allowed us to estimate the lensed galaxy redshift to a better accuracy than pre-ALMA estimates and to model the emission of the optical, mm, and X-ray band emission for this galaxy. We demonstrated that the X-ray emission is generated in the nuclear environment and it strongly support the presence of nuclear activity in this object. Hence, we identified weak nuclear activity associated with high-z galaxies with large star formation rates, useful to extend the investigation of the relationship between star formation and nuclear activity to two intrinsically less luminous, high-z star forming galaxies than was possible so far. Given our results only for two objects, they solely cannot constrain the evolutionary models, but provide us with interesting hints and set an observational path towards addressing the role of star formation and nuclear activity in forming galaxies.

astro-ph.GA↗

arXiv2017

Witnessing the birth of the red sequence: the physical scale and morphology of dust emission in hyper-luminous starbursts in the early Universe

We present high-spatial-resolution ($\sim 0.12''$ or $\approx 800 \, {\rm pc}$ at $z = 4.5$) ALMA $870\,μ$m dust continuum observations of a sample of 44 ultrared dusty star-forming galaxies (DSFGs) selected from the H-ATLAS and HerMES far-infrared surveys because of their red colors from 250 to 500 $μ$m: $S_{500} / S_{250} > 1.5$ and $S_{500} / S_{350} > 1.0$. With photometric redshifts in the range $z \sim 4$-6, our sample includes the most luminous starbursting systems in the early Universe known so far, with total obscured star-formation rates (SFRs) of up to $\sim 4,500 \, M_\odot \, {\rm yr}^{-1}$, as well as a population of lensed, less intrinsically luminous sources. The lower limit on the number of ultrared DSFGs at 870 $μ$m (with flux densities measured from the ALMA maps and thus not affected by source confusion) derived in this work is in reasonable agreement with models of galaxy evolution, whereas there have been reports of conflicts at 500 $μ$m (where flux densities are derived from SPIRE). Ultrared DSFGs have a variety of morphologies (from relatively extended disks with smooth radial profiles, to compact sources, both isolated and interacting) and an average size, $θ_{\rm FWHM}$, of $1.46 \pm 0.41\, {\rm kpc}$, considerably smaller than the values reported in previous work for less-luminous DSFGs at lower redshifts. The size and the estimated gas-depletion times of our sources are compatible with their being the progenitors of the most massive, compact, red-and-dead galaxies at $z \sim 2$-3, and ultimately of local ultra-massive elliptical galaxies or massive galaxy clusters. We are witnessing the birth of the high-mass tail of the red sequence of galaxies.

astro-ph.GA↗

arXiv2017

The Herschel Bright Sources (HerBS): Sample definition and SCUBA-2 observations

We present the Herschel Bright Sources (HerBS) sample, a sample of bright, high-redshift Herschel sources detected in the 616.4 square degree H-ATLAS survey. The HerBS sample contains 209 galaxies, selected with a 500 μm flux density greater than 80 mJy and an estimated redshift greater than 2. The sample consists of a combination of HyLIRGs and lensed ULIRGs during the epoch of peak cosmic star formation. In this paper, we present SCUBA-2 observations at 850 $μ$m of 189 galaxies of the HerBS sample, 152 of these sources were detected. We fit a spectral template to the Herschel-SPIRE and 850 $μ$m SCUBA-2 flux densities of 22 sources with spectroscopically determined redshifts, using a two-component modified blackbody spectrum as a template. We find a cold- and hot-dust temperature of 21.29 K and 45.80 K, a cold-to-hot dust mass ratio of 26.62 and a $β$ of 1.83. The poor quality of the fit suggests that the sample of galaxies is too diverse to be explained by our simple model. Comparison of our sample to a galaxy evolution model indicates that the fraction of lenses is high. Out of the 152 SCUBA-2 detected galaxies, the model predicts 128.4 $\pm$ 2.1 of those galaxies to be lensed (84.5%). The SPIRE 500 $μ$m flux suggests that out of all 209 HerBS sources, we expect 158.1 $\pm$ 1.7 lensed sources, giving a total lensing fraction of 76 per cent.

astro-ph.GA↗

arXiv2017

Exploring cosmic origins with CORE: effects of observer peculiar motion

We discuss the effects on the CMB, CIB, and thermal SZ effect due to the peculiar motion of an observer with respect to the CMB rest frame, which induces boosting effects. We investigate the scientific perspectives opened by future CMB space missions, focussing on the CORE proposal. The improvements in sensitivity offered by a mission like CORE, together with its high resolution over a wide frequency range, will provide a more accurate estimate of the CMB dipole. The extension of boosting effects to polarization and cross-correlations will enable a more robust determination of purely velocity-driven effects that are not degenerate with the intrinsic CMB dipole, allowing us to achieve a S/N ratio of 13; this improves on the Planck detection and essentially equals that of an ideal cosmic-variance-limited experiment up to a multipole l of 2000. Precise inter-frequency calibration will offer the opportunity to constrain or even detect CMB spectral distortions, particularly from the cosmological reionization, because of the frequency dependence of the dipole spectrum, without resorting to precise absolute calibration. The expected improvement with respect to COBE-FIRAS in the recovery of distortion parameters (in principle, a factor of several hundred for an ideal experiment with the CORE configuration) ranges from a factor of several up to about 50, depending on the quality of foreground removal and relative calibration. Even for 1% accuracy in both foreground removal and relative calibration at an angular scale of 1 deg, we find that dipole analyses for a mission like CORE will be able to improve the recovery of the CIB spectrum amplitude by a factor of 17 in comparison with current results based on FIRAS. In addition to the scientific potential of a mission like CORE for these analyses, synergies with other planned and ongoing projects are also discussed.

astro-ph.CO↗

arXiv2017

Exploring cosmic origins with CORE: mitigation of systematic effects

We present an analysis of the main systematic effects that could impact the measurement of CMB polarization with the proposed CORE space mission. We employ timeline-to-map simulations to verify that the CORE instrumental set-up and scanning strategy allow us to measure sky polarization to a level of accuracy adequate to the mission science goals. We also show how the CORE observations can be processed to mitigate the level of contamination by potentially worrying systematics, including intensity-to-polarization leakage due to bandpass mismatch, asymmetric main beams, pointing errors and correlated noise. We use analysis techniques that are well validated on data from current missions such as Planck to demonstrate how the residual contamination of the measurements by these effects can be brought to a level low enough not to hamper the scientific capability of the mission, nor significantly increase the overall error budget. We also present a prototype of the CORE photometric calibration pipeline, based on that used for Planck, and discuss its robustness to systematics, showing how CORE can achieve its calibration requirements. While a fine-grained assessment of the impact of systematics requires a level of knowledge of the system that can only be achieved in a future study phase, the analysis presented here strongly suggests that the main areas of concern for the CORE mission can be addressed using existing knowledge, techniques and algorithms.

astro-ph.CO↗

arXiv2017

Herschel and Hubble study of a lensed massive dusty starbursting galaxy at $z\sim3$

We present the results of combined deep Keck/NIRC2, HST/WFC3 near-infrared and Herschel far infrared observations of an extremely star forming dusty lensed galaxy identified from the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS J133542.9+300401). The galaxy is gravitationally lensed by a massive WISE identified galaxy cluster at $z\sim1$. The lensed galaxy is spectroscopically confirmed at $z=2.685$ from detection of $\rm {CO (1 \rightarrow 0)}$ by GBT and from detection of $\rm {CO (3 \rightarrow 2)}$ obtained with CARMA. We use the combined spectroscopic and imaging observations to construct a detailed lens model of the background dusty star-forming galaxy (DSFG) which allows us to study the source plane properties of the target. The best-fit lens model provide magnification of $μ_{\rm star}=2.10\pm0.11$ and $μ_{\rm dust}=2.02\pm0.06$ for the stellar and dust components respectively. Multi-band data yields a magnification corrected star formation rate of $1900(\pm200)\,M_{\odot}{\rm yr^{-1}}$ and stellar mass of $6.8_{-2.7}^{+0.9}\times10^{11}\,M_{\odot}$ consistent with a main sequence of star formation at $z\sim2.6$. The CO observations yield a molecular gas mass of $8.3(\pm1.0)\times10^{10}\,M_{\odot}$, similar to the most massive star-forming galaxies, which together with the high star-formation efficiency are responsible for the intense observed star formation rates. The lensed DSFG has a very short gas depletion time scale of $\sim40$ Myr. The high stellar mass and small gas fractions observed indicate that the lensed DSFG likely has already formed most of its stellar mass and could be a progenitor of the most massive elliptical galaxies found in the local Universe.

astro-ph.GA↗

arXiv2017

Exploring Cosmic Origins with CORE: B-mode Component Separation

We demonstrate that, for the baseline design of the CORE satellite mission, the polarized foregrounds can be controlled at the level required to allow the detection of the primordial cosmic microwave background (CMB) $B$-mode polarization with the desired accuracy at both reionization and recombination scales, for tensor-to-scalar ratio values of ${r\gtrsim 5\times 10^{-3}}$. We consider detailed sky simulations based on state-of-the-art CMB observations that consist of CMB polarization with $τ=0.055$ and tensor-to-scalar values ranging from $r=10^{-2}$ to $10^{-3}$, Galactic synchrotron, and thermal dust polarization with variable spectral indices over the sky, polarized anomalous microwave emission, polarized infrared and radio sources, and gravitational lensing effects. Using both parametric and blind approaches, we perform full component separation and likelihood analysis of the simulations, allowing us to quantify both uncertainties and biases on the reconstructed primordial $B$-modes. Under the assumption of perfect control of lensing effects, CORE would measure an unbiased estimate of $r=\left(5 \pm 0.4\right)\times 10^{-3}$ after foreground cleaning. In the presence of both gravitational lensing effects and astrophysical foregrounds, the significance of the detection is lowered, with CORE achieving a $4σ$-measurement of $r=5\times 10^{-3}$ after foreground cleaning and $60$% delensing. For lower tensor-to-scalar ratios ($r=10^{-3}$) the overall uncertainty on $r$ is dominated by foreground residuals, not by the 40% residual of lensing cosmic variance. Moreover, the residual contribution of unprocessed polarized point-sources can be the dominant foreground contamination to primordial B-modes at this $r$ level, even on relatively large angular scales, $\ell \sim 50$. Finally, we report two sources of potential bias for the detection of the primordial $B$-modes.[abridged]

astro-ph.CO↗

arXiv2017

On the statistics of proto-cluster candidates detected in the Planck all-sky survey

Observational investigations of the abundance of massive precursors of local galaxy clusters ("proto-clusters") allow us to test the growth of density perturbations, to constrain cosmological parameters that control it, to test the theory of non-linear collapse and how the galaxy formation takes place in dense environments. The Planck collaboration has recently published a catalogue of >~ 2000 cold extra-galactic sub-millimeter sources, i.e. with colours indicative of z >~ 2, almost all of which appear to be over-densities of star-forming galaxies. They are thus considered as proto-cluster candidates. Their number densities (or their flux densities) are far in excess of expectations from the standard scenario for the evolution of large-scale structure. Simulations based on a physically motivated galaxy evolution model show that essentially all cold peaks brighter than S_{545GHz} = 500 mJy found in Planck maps after having removed the Galactic dust emission can be interpreted as positive Poisson fluctuations of the number of high-z dusty proto-clusters within the same Planck beam, rather then being individual clumps of physically bound galaxies. This conclusion does not change if an empirical fit to the luminosity function of dusty galaxies is used instead of the physical model. The simulations accurately reproduce the statistic of the Planck detections and yield distributions of sizes and ellipticities in qualitative agreement with observations. The redshift distribution of the brightest proto-clusters contributing to the cold peaks has a broad maximum at 1.5 <~ z <~ 3. Therefore follow-up of Planck proto-cluster candidates will provide key information on the high-z evolution of large scale structure.

astro-ph.GA↗

arXiv2017

Exploring Cosmic Origins with CORE: Extragalactic sources in Cosmic Microwave Background maps

We discuss the potential of a next generation space-borne Cosmic Microwave Background (CMB) experiment for studies of extragalactic sources. Our analysis has particular bearing on the definition of the future space project, CORE, that has been submitted in response to ESA's call for a Medium-size mission opportunity as the successor of the Planck satellite. Even though the effective telescope size will be somewhat smaller than that of Planck, CORE will have a considerably better angular resolution at its highest frequencies, since, in contrast with Planck, it will be diffraction limited at all frequencies. The improved resolution implies a considerable decrease of the source confusion, i.e. substantially fainter detection limits. In particular, CORE will detect thousands of strongly lensed high-z galaxies distributed over the full sky. The extreme brightness of these galaxies will make it possible to study them, via follow-up observations, in extraordinary detail. Also, the CORE resolution matches the typical sizes of high-z galaxy proto-clusters much better than the Planck resolution, resulting in a much higher detection efficiency; these objects will be caught in an evolutionary phase beyond the reach of surveys in other wavebands. Furthermore, CORE will provide unique information on the evolution of the star formation in virialized groups and clusters of galaxies up to the highest possible redshifts. Finally, thanks to its very high sensitivity, CORE will detect the polarized emission of thousands of radio sources and, for the first time, of dusty galaxies, at mm and sub-mm wavelengths, respectively.

astro-ph.GA↗

arXiv2017

Exploring Cosmic Origins with CORE: Cluster Science

We examine the cosmological constraints that can be achieved with a galaxy cluster survey with the future CORE space mission. Using realistic simulations of the millimeter sky, produced with the latest version of the Planck Sky Model, we characterize the CORE cluster catalogues as a function of the main mission performance parameters. We pay particular attention to telescope size, key to improved angular resolution, and discuss the comparison and the complementarity of CORE with ambitious future ground-based CMB experiments that could be deployed in the next decade. A possible CORE mission concept with a 150 cm diameter primary mirror can detect of the order of 50,000 clusters through the thermal Sunyaev-Zeldovich effect (SZE). The total yield increases (decreases) by 25% when increasing (decreasing) the mirror diameter by 30 cm. The 150 cm telescope configuration will detect the most massive clusters ($>10^{14}\, M_\odot$) at redshift $z>1.5$ over the whole sky, although the exact number above this redshift is tied to the uncertain evolution of the cluster SZE flux-mass relation; assuming self-similar evolution, CORE will detect $\sim 500$ clusters at redshift $z>1.5$. This changes to 800 (200) when increasing (decreasing) the mirror size by 30 cm. CORE will be able to measure individual cluster halo masses through lensing of the cosmic microwave background anisotropies with a 1-$σ$ sensitivity of $4\times10^{14} M_\odot$, for a 120 cm aperture telescope, and $10^{14} M_\odot$ for a 180 cm one. [abridged]

astro-ph.CO↗

arXiv2017

High dense gas fraction in intensely star-forming dusty galaxies at high redshift

We present ALMA and VLA detections of the dense molecular gas tracers HCN, HCO$^+$ and HNC in two lensed, high-redshift starbursts selected from the {\it Herschel}-ATLAS survey: {\it H}-ATLAS\,J090740.0$-$004200 (SDP.9, $z \sim 1.6$) and {\it H}-ATLAS\,J091043.1$-$000321 (SDP.11, $z \sim 1.8$). ALMA observed the $J = 3-2$ transitions in both sources, while the VLA observed the $J = 1-0$ transitions in SDP.9. We have detected all observed HCN and HCO$^+$ lines in SDP.9 and SDP.11, and also HNC(3--2) in SDP.9. The amplification factors for both galaxies have been determined from sub-arcsec resolution CO and dust emission observations carried out with NOEMA and the SMA. The HNC(1--0)/HCN(1--0) line ratio in SDP.9 suggests the presence of photon-dominated regions, as it happens to most local (U)LIRGs. The CO, HCN and HCO$^+$ SLEDs of SDP.9 are compatible to those found for many local, infrared (IR) bright galaxies, indicating that the molecular gas in local and high-redshift dusty starbursts can have similar excitation conditions. We obtain that the correlation between total IR ($L_{\rm IR}$) and dense line ($L_{\rm dense}$) luminosity in SDP.9 and SDP.11 and local star-forming galaxies can be represented by a single relation. The scatter of the $L_{\rm IR} - L_{\rm dense}$ correlation, together with the lack of sensitive dense molecular gas tracer observations for a homogeneous sample of high-redshift galaxies, prevents us from distinguishing differential trends with redshift. Our results suggest that the intense star formation found in some high-redshift dusty, luminous starbursts is associated with more massive dense molecular gas reservoirs and higher dense molecular gas fractions.

astro-ph.GA↗

arXiv2016

The Herschel-ATLAS: a sample of 500μm-selected lensed galaxies over 600 square degrees

We present a sample of 80 candidate strongly lensed galaxies with flux density above 100mJy at 500μm extracted from the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS), over an area of 600 square degrees. Available imaging and spectroscopic data allow us to confirm the strong lensing in 20 cases and to reject it in one case. For other 8 objects the lensing scenario is strongly supported by the presence of two sources along the same line of sight with distinct photometric redshifts. The remaining objects await more follow-up observations to confirm their nature. The lenses and the background sources have median redshifts z_L = 0.6 and z_S = 2.5, respectively, and are observed out to z_L = 1.2 and z_S = 4.2. We measure the number counts of candidate lensed galaxies at 500μm and compare them with theoretical predictions, finding a good agreement for a maximum magnification of the background sources in the range 10-20. These values are consistent with the magnification factors derived from the lens modelling of individual systems. The catalogue presented here provides sub- mm bright targets for follow-up observations aimed at exploiting gravitational lensing to study with un-precedented details the morphological and dynamical properties of dusty star forming regions in z >~ 1.5 galaxies.

astro-ph.GA↗

arXiv2016

The space density of luminous dusty star-forming galaxies at $z>4$: SCUBA-2 and LABOCA imaging of ultrared galaxies from $Herschel$-ATLAS

Until recently, only a handful of dusty, star-forming galaxies (DSFGs) were known at $z>4$, most of them significantly amplified by gravitational lensing. Here, we have increased the number of such DSFGs substantially, selecting galaxies from the uniquely wide 250-, 350- and 500-$μ$m Herschel-ATLAS imaging survey on the basis of their extremely red far-infrared colors and faint 350- and 500-$μ$m flux densities - ergo they are expected to be largely unlensed, luminous, rare and very distant. The addition of ground-based continuum photometry at longer wavelengths from the JCMT and APEX allows us to identify the dust peak in their SEDs, better constraining their redshifts. We select the SED templates best able to determine photometric redshifts using a sample of 69 high-redshift, lensed DSFGs, then perform checks to assess the impact of the CMB on our technique, and to quantify the systematic uncertainty associated with our photometric redshifts, $σ=0.14\,(1+z)$, using a sample of 25 galaxies with spectroscopic redshifts, each consistent with our color selection. For Herschel-selected ultrared galaxies with typical colors of $S_{500}/S_{250}\sim 2.2$ and $S_{500}/S_{350}\sim 1.3$ and flux densities, $S_{500}\sim 50\,$mJy, we determine a median redshift, $\hat{z}_{\rm phot}=3.66$, an interquartile redshift range, 3.30$-$4.27, with a median rest-frame 8$-$1000-$μ$m luminosity, $\hat{L}_{\rm IR}$, of $1.3\times 10^{13}\,$L$_\odot$. A third lie at $z>4$, suggesting a space density, $ρ_{z>4}$, of $\approx 6 \times 10^{-7}\,$Mpc$^{-3}$. Our sample contains the most luminous known star-forming galaxies, and the most over-dense cluster of starbursting proto-ellipticals yet found.

astro-ph.GA↗

arXiv2016

Tracing black hole accretion with SED decomposition and IR lines: from local galaxies to the high-z Universe

We present new estimates of AGN accretion and star-formation luminosity in galaxies obtained for the local 12-$μ$m sample of Seyfert galaxies (12MGS), by performing a detailed broad-band spectral energy distribution (SED) decomposition including the emission of stars, dust heated by star formation and a possible AGN dusty torus. Thanks to the availability of data from the X-rays to the sub-millimetre, we constrain and test the contribution of the stellar, AGN and star-formation components to the SEDs. The availability of Spitzer-IRS low resolution mid-infrared (mid-IR) spectra is crucial to constrain the dusty torus component at its peak wavelengths. The results of SED-fitting are also tested against the available information in other bands: the reconstructed AGN bolometric luminosity is compared to those derived from X-rays and from the high excitation IR lines tracing AGN activity like [Ne V] and [O IV]. The IR luminosity due to star-formation (SF) and the intrinsic AGN bolometric luminosity are shown to be strongly related to the IR line luminosity. Variations of these relations with different AGN fractions are investigated, showing that the relation dispersions are mainly due to different AGN relative contribution within the galaxy. Extrapolating these local relations between line and SF or AGN luminosities to higher redshifts, by means of recent Herschel galaxy evolution results, we then obtain mid- and far-IR line luminosity functions useful to estimate how many star-forming galaxies and AGN we expect to detect in the different lines at different redshifts and luminosities with future IR facilities (e.g., JWST, SPICA).

astro-ph.GA↗

arXiv2016

Another look to distortions of the CMB spectrum

We review aspects of Cosmic Microwave Background (CMB) spectral distortions which do not appear to have been fully explored in the literature. In particular, implications of recent evidences of heating of the intergalactic medium (IGM) by feedback from active galactic nuclei are investigated. Taking also into account the IGM heating associated to structure formation, we argue that values of the y parameter of several*10^(-6), i.e. a factor of a few below the COBE/FIRAS upper limit, are to be expected. The Compton scattering by the re-ionized plasma also re-processes primordial distortions, adding a y-type contribution. Hence no pure Bose-Einstein-like distortions are to be expected. An assessment of Galactic and extragalactic foregrounds, taking into account the latest results from the Planck satellite as well as the contributions from the strong CII and CO lines from star-forming galaxies, demonstrates that a foreground subtraction accurate enough to fully exploit the PIXIE sensitivity will be extremely challenging. Motivated by this fact we also discuss methods to detect spectral distortions not requiring absolute measurements and show that accurate determinations of the frequency spectrum of the CMB dipole amplitude may substantially improve over COBE/FIRAS limits on distortion parameters. Such improvements may be at reach of next generation CMB anisotropy experiments. The estimated amplitude of the Cosmic Infrared Background (CIB) dipole might be detectable by careful analyses of Planck maps at the highest frequencies. Thus Planck might provide interesting constraints on the CIB intensity, currently known with a ~30% uncertainty.

astro-ph.CO↗

arXiv2015

ALMA constraints on the faint millimetre source number counts and their contribution to the cosmic infrared background

We have analysed 18 ALMA continuum maps in Bands 6 and 7, with rms down to 7.8$μ$Jy, to derive differential number counts down to 60$μ$Jy and 100$μ$Jy at $λ=$1.3 mm and $λ=$1.1 mm, respectively. The area covered by the combined fields is $\rm 9.5\times10^{-4}deg^2$ at 1.1mm and $\rm 6.6\times10^{-4}deg^{2}$ at 1.3mm. We improved the source extraction method by requiring that the dimension of the detected sources be consistent with the beam size. This method enabled us to remove spurious detections that have plagued the purity of the catalogues in previous studies. We detected 50 faint sources with S/N$>$3.5 down to 60$μ$Jy, hence improving the statistics by a factor of four relative to previous studies. The inferred differential number counts are $\rm dN/d(Log_{10}S)=1\times10^5~deg^2$ at a 1.1 mm flux $S_{λ= 1.1~mm} = 130~μ$Jy, and $\rm dN/d(Log_{10}S)=1.1\times10^5~deg^2$ at a 1.3 mm flux $\rm S_{λ= 1.3~mm} = 60~μ$Jy. At the faintest flux limits, i.e. 30$μ$Jy and 40$μ$Jy, we obtain upper limits on the differential number counts of $\rm dN/d(Log_{10}S) < 7\times10^5~deg^2$ and $\rm dN/d(Log_{10}S)<3\times10^5~deg^2$, respectively. Our results provide a new lower limit to CIB intensity of 17.2${\rm Jy\ deg^{-2}}$ at 1.1mm and of 12.9${\rm Jy\ deg^{-2}}$ at 1.3mm. Moreover, the flattening of the integrated number counts at faint fluxes strongly suggests that we are probably close to the CIB intensity. Our data imply that galaxies with SFR$<40~M_{\odot}/yr$ certainly contribute less than 50% to the CIB while more than 50% of the CIB must be produced by galaxies with $\rm SFR>40~M_{\odot}/yr$. The differential number counts are in nice agreement with recent semi-analytical models of galaxy formation even as low as our faint fluxes. Consequently, this supports the galaxy evolutionary scenarios and assumptions made in these models.

astro-ph.GA↗

arXiv2015

Revealing the complex nature of the strong gravitationally lensed system H-ATLAS J090311.6+003906 using ALMA

We have modelled Atacama Large Millimeter/sub-millimeter Array (ALMA) long baseline imaging of the strong gravitational lens system H-ATLAS J090311.6+003906 (SDP.81). We have reconstructed the distribution of band 6 and 7 continuum emission in the z=3.042 source and we have determined its kinematic properties by reconstructing CO(5-4) and CO(8-7) line emission in bands 4 and 6. The continuum imaging reveals a highly non-uniform distribution of dust with clumps on scales of 200 pc. In contrast, the CO line emission shows a relatively smooth, disk-like velocity field which is well fit by a rotating disk model with an inclination angle of 40+/-5 degrees and an asymptotic rotation velocity of 320 km/s. The inferred dynamical mass within 1.5kpc is (3.5+/-0.5)x10^{10} M_sol which is comparable to the total molecular gas masses of (2.7+/-0.5)x10^{10} M_sol and (3.5+/-0.6)x10^{10} M_sol from the dust continuum emission and CO emission respectively. Our new reconstruction of the lensed HST near-infrared emission shows two objects which appear to be interacting, with the rotating disk of gas and dust revealed by ALMA distinctly offset from the near-infrared emission. The clumpy nature of the dust and a low value of the Toomre parameter of Q=0.3 suggest that the disk is in a state of collapse. We estimate a star formation rate in the disk of 470+/-80 M_sol/yr with an efficiency 65 times greater than typical low-redshift galaxies. Our findings add to the growing body of evidence that the most infra-red luminous, dust obscured galaxies in the high redshift Universe represent a population of merger induced starbursts.

astro-ph.GA↗

arXiv2015

Predictions for surveys with the SPICA Mid-infrared Instrument

We present predictions for number counts and redshift distributions of galaxies detectable in continuum and in emission lines with the Mid-infrared (MIR) Instrument (SMI) proposed for the Space Infrared Telescope for Cosmology and Astrophysics (SPICA). We have considered 24 MIR fine-structure lines, four Polycyclic Aromatic Hydrocarbon (PAH) bands (at 6.2, 7.7, 8.6 and 11.3$μ$m) and two silicate bands (in emission and in absorption) at 9.7$μ$m and 18.0$μ$m. Six of these lines are primarily associated with Active Galactic Nuclei (AGNs), the others with star formation. A survey with the SMI spectrometers of 1 hour integration per field-of-view (FoV) over an area of $1\,\hbox{deg}^2$ will yield $5\,σ$ detections of $\simeq 140$ AGN lines and of $\simeq 5.2\times10^{4}$ star-forming galaxies, $\simeq 1.6\times10^{4}$ of which will be detected in at least two lines. The combination of a shallow ($20.0\,\hbox{deg}^{2}$, $1.4\times10^{-1}$ h integration per FoV) and a deep survey ($6.9\times10^{-3}\,\hbox{deg}^{2}$, $635$ h integration time), with the SMI camera, for a total of $\sim$1000 h, will accurately determine the MIR number counts of galaxies and of AGNs over five orders of magnitude in flux density, reaching values more than one order of magnitude fainter than the deepest Spitzer $24\,μ$m surveys. This will allow us to determine the cosmic star formation rate (SFR) function down to SFRs more than 100 times fainter than reached by the Herschel Observatory.

astro-ph.GA↗