arXiv subjects

D. Lutz

Publications and source records attributed to D. Lutz.

At least 199 records · Page 11Linked to original sources

arXiv2012

Excited OH+, H2O+, and H3O+ in NGC 4418 and Arp 220

We report on Herschel/PACS observations of absorption lines of OH+, H2O+ and H3O+ in NGC 4418 and Arp 220. Excited lines of OH+ and H2O+ with E_lower of at least 285 and \sim200 K, respectively, are detected in both sources, indicating radiative pumping and location in the high radiation density environment of the nuclear regions. Abundance ratios OH+/H2O+ of 1-2.5 are estimated in the nuclei of both sources. The inferred OH+ column and abundance relative to H nuclei are (0.5-1)x10^{16} cm-2 and \sim2x10^{-8}, respectively. Additionally, in Arp 220, an extended low excitation component around the nuclear region is found to have OH+/H2O+\sim5-10. H3O+ is detected in both sources with N(H3O+)\sim(0.5-2)x10^{16} cm-2, and in Arp 220 the pure inversion, metastable lines indicate a high rotational temperature of ~500 K, indicative of formation pumping and/or hot gas. Simple chemical models favor an ionization sequence dominated by H+ - O+ - OH+ - H2O+ - H3O+, and we also argue that the H+ production is most likely dominated by X-ray/cosmic ray ionization. The full set of observations and models leads us to propose that the molecular ions arise in a relatively low density (\gtrsim10^4 cm-3) interclump medium, in which case the ionization rate per H nucleus (including secondary ionizations) is zeta>10^{-13} s-1, a lower limit that is severalx10^2 times the highest rate estimates for Galactic regions. In Arp 220, our lower limit for zeta is compatible with estimates for the cosmic ray energy density inferred previously from the supernova rate and synchrotron radio emission, and also with the expected ionization rate produced by X-rays. In NGC 4418, we argue that X-ray ionization due to an AGN is responsible for the molecular ion production.

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arXiv2012

The effect of the high-pass filter data reduction technique on the Herschel PACS Photometer PSF and noise

We investigate the effect of the "high-pass filter" data reduction technique on the Herschel PACS PSF and noise of the PACS maps at the 70, 100 and 160 um bands and in medium and fast scan speeds. This branch of the PACS Photometer pipeline is the most used for cosmological observations and for point-source observations.The calibration of the flux loss due to the median removal applied by the PACS pipeline (high-pass filter) is done via dedicated simulations obtained by "polluting" real PACS timelines with fake sources at different flux levels. The effect of the data reduction parameter settings on the final map noise is done by using selected observations of blank fields with high data redundancy. We show that the running median removal can cause significant flux losses at any flux level. We analyse the advantages and disadvantages of several masking strategies and suggest that a mask based on putting circular patches on prior positions is the best solution to reduce the amount of flux loss. We provide a calibration of the point-source flux loss for several masking strategies in a large range of data reduction parameters, and as a function of the source flux. We also show that, for stacking analysis, the impact of the high-pass filtering effect is to reduce significantly the clustering effect. The analysis of the global noise and noise components of the PACS maps shows that the dominant parameter in determining the final noise is the high-pass filter width. We also provide simple fitting functions to build the error map from the coverage map and to estimate the cross-correlation correction factor in a representative portion of the data reduction parameter space.

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arXiv2012

A Population of z>2 Far-Infrared Herschel-SPIRE selected Starbursts

We present spectroscopic observations for a sample of 36 Herschel-SPIRE 250-500um selected galaxies (HSGs) at 2 2 HyLIRGs in the literature which are detected serendipitously or via tailored surveys searching only for high-z HyLIRGs; therefore, we can place lower limits on the contribution of HSGs to the cosmic star formation rate density at (7+-2)x10^(-3)Msun/yr h^3Mpc^(-3) at z~2.5, which is >10% of the estimated total star formation rate density (SFRD) of the Universe from optical surveys. The contribution at z~4 has a lower limit of 3x10^(-3)Msun/yr h^3 Mpc^(-3), ~>20% of the estimated total SFRD. This highlights the importance of extremely infrared-luminous galaxies with high star formation rates to the build-up of stellar mass, even at the earliest epochs.

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arXiv2012

A Redshift Survey of Herschel Far-Infrared Selected Starbursts and Implications for Obscured Star Formation

We present Keck spectroscopic observations and redshifts for a sample of 767 Herschel-SPIRE selected galaxies (HSGs) at 250, 350, and 500um, taken with the Keck I Low Resolution Imaging Spectrometer (LRIS) and the Keck II DEep Imaging Multi-Object Spectrograph (DEIMOS). The redshift distribution of these SPIRE sources from the Herschel Multitiered Extragalactic Survey (HerMES) peaks at z=0.85, with 731 sources at z<2 and a tail of sources out to z~5. We measure more significant disagreement between photometric and spectroscopic redshifts ( /(1+z)>=0.29) than is seen in non-infrared selected samples, likely due to enhanced star formation rates and dust obscuration in infrared-selected galaxies. We estimate that the vast majority (72-83%) of z<2 Herschel-selected galaxies would drop out of traditional submillimeter surveys at 0.85-1mm. We estimate the luminosity function and implied star-formation rate density contribution of HSGs at z<1.6 and find overall agreement with work based on 24um extrapolations of the LIRG, ULIRG and total infrared contributions. This work significantly increased the number of spectroscopically confirmed infrared-luminous galaxies at z>>0 and demonstrates the growing importance of dusty starbursts for galaxy evolution studies and the build-up of stellar mass throughout cosmic time. [abridged]

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arXiv2012

Spectroscopic FIR mapping of the disk and galactic wind of M82 with Herschel-PACS

[Abridged] We present maps of the main cooling lines of the neutral atomic gas ([OI] at 63 and 145 micron and [CII] at 158 micron) and in the [OIII] 88 micron line of the starburst galaxy M82, carried out with the PACS spectrometer on board the Herschel satellite. By applying PDR modeling we derive maps of the main ISM physical parameters, including the [CII] optical depth, at unprecedented spatial resolution (~300 pc). We can clearly kinematically separate the disk from the outflow in all lines. The [CII] and [OI] distributions are consistent with PDR emission both in the disk and in the outflow. Surprisingly, in the outflow, the atomic and the ionized gas traced by the [OIII] line both have a deprojected velocity of ~75 km/s, very similar to the average velocity of the outflowing cold molecular gas (~ 100 km/s) and several times smaller than the outflowing material detected in Halpha (~ 600 km/s). This suggests that the cold molecular and neutral atomic gas and the ionized gas traced by the [OIII] 88 micron line are dynamically coupled to each other but decoupled from the Halpha emitting gas. We propose a scenario where cold clouds from the disk are entrained into the outflow by the winds where they likely evaporate, surviving as small, fairly dense cloudlets (n_H\sim 500-1000 cm^-3, G_0\sim 500- 1000, T_gas\sim300 K). We show that the UV photons provided by the starburst are sufficient to excite the PDR shells around the molecular cores. The mass of the neutral atomic gas in the outflow is \gtrsim 5-12x 10^7 M_sun to be compared with that of the molecular gas (3.3 x 10^8 M_sun) and of the Halpha emitting gas (5.8 x 10^6 M_sun). The mass loading factor, (dM/dt)/SFR, of the molecular plus neutral atomic gas in the outflow is ~ 2. Energy and momentum driven outflow models can explain the data equally well, if all the outflowing gas components are taken into account.

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arXiv2012

Dust temperature and CO-to-H2 conversion factor variations in the SFR-M* plane

Deep Herschel imaging and 12CO(2-1) line luminosities from the IRAM PdBI are combined for a sample of 17 galaxies at z>1 from the GOODS-N field. The sample includes galaxies both on and above the main sequence (MS) traced by star-forming galaxies in the SFR-M* plane. The far-infrared data are used to derive dust masses, Mdust. Combined with an empirical prescription for the dependence of the gas-to-dust ratio on metallicity (GDR), the CO luminosities and Mdust values are used to derive for each galaxy the CO-to-H2 conversion factor, alpha_co. Like in the local Universe, the value of alpha_co is a factor of ~5 smaller in starbursts compared to normal star-forming galaxies (SFGs). We also uncover a relation between alpha_co and dust temperature (Tdust; alpha_co decreasing with increasing Tdust) as obtained from modified blackbody fits to the far-infrared data. While the absolute normalization of the alpha_co(Tdust) relation is uncertain, the global trend is robust against possible systematic biases in the determination of Mdust, GDR or metallicity. Although we cannot formally distinguish between a step and a smooth evolution of alpha_co with the dust temperature, we can conclude that in galaxies of near-solar metallicity, a critical value of Tdust=30K can be used to determine whether the appropriate alpha_co is closer to the starburst value (1.0 Msun(K kms pc^2)^-1, if Tdust>30K) or closer to the Galactic value (4.35 Msun (K kms pc^2)^-1, if Tdust<30K). This indicator has the great advantage of being less subjective than visual morphological classifications of mergers/SFGs, which can be difficult at high z because of the clumpy nature of SFGs. In the absence of far-infrared data, the offset of a galaxy from the main sequence (i.e., log[SSFR(galaxy)/SSFR_MS(M*,z)]) can be used to identify galaxies requiring the use of an alpha_co conversion factor lower than the Galactic value.

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arXiv2012

Cosmic Evolution of Star-Formation Enhancement in Close Major-Merger Galaxy Pairs Since z = 1

The infrared (IR) emission of M_* galaxies (10^{10.4} < M_{star} < 10^{11.0} M_\sun) in galaxy pairs, derived using data obtained in Herschel (PEP/HerMES) and Spitzer (S-COSMOS) surveys, is compared to that of single disk galaxies in well matched control samples to study the cosmic evolution of the star-formation enhancement induced by galaxy-galaxy interaction. Both the mean IR SED and mean IR luminosity of star-forming galaxies (SFGs) in SFG+SFG (S+S) pairs in the redshift bin of 0.6 < z < 1 are consistent with no star-formation enhancement. SFGs in S+S pairs in a lower redshift bin of 0.2 < z < 0.6 show marginal evidence for a weak star-formation enhancement. Together with the significant and strong sSFR enhancement shown by SFGs in a local sample of S+S pairs (obtained using previously published Spitzer observations), our results reveal a trend for the star-formation enhancement in S+S pairs to decrease with increasing redshift. Between z=0 and z=1, this decline of interaction-induced star-formation enhancement occurs in parallel with the dramatic increase (by a factor of ~10) of the sSFR of single SFGs, both can be explained by the higher gas fraction in higher z disks. SFGs in mixed pairs (S+E pairs) do not show any significant star-formation enhancement at any redshift. The difference between SFGs in S+S pairs and in S+E pairs suggests a modulation of the sSFR by the inter-galactic medium IGM in the dark matter halos (DMH) hosting these pairs.

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arXiv2012

Near-Infrared spectroscopy of the super star cluster in NGC1705

We study the near-infrared properties of the super star cluster NGC1750-1 in order to constrain its spatial extent, its stellar population and its age. We use adaptive optics assisted integral field spectroscopy with SINFONI on the VLT. We estimate the spatial extent of the cluster and extract its K-band spectrum from which we constrain the age of the dominant stellar population. Our observations have an angular resolution of about 0.11", providing an upper limit on the cluster radius of 2.85+/-0.50 pc depending on the assumed distance. The K-band spectrum is dominated by strong CO absorption bandheads typical of red supergiants. Its spectral type is equivalent to a K4-5I star. Using evolutionary tracks from the Geneva and Utrecht groups, we determine an age of 12+/-6 Myr. The large uncertainty is rooted in the large difference between the Geneva and Utrecht tracks in the red supergiants regime. The absence of ionized gas lines in the K-band spectrum is consistent with the absence of O and/or Wolf-Rayet stars in the cluster, as expected for the estimated age.

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arXiv2012

Accreting SMBHs in the COSMOS field and the connection to their host galaxies

Using the wide multi-band photometry available in the COSMOS field we explore the host galaxy properties of a large sample of Active Galactic Nuclei (AGN) obtained by combining X-ray and optical spectroscopic selections. Based on a careful study of their Spectral Energy Distribution (SED), which has been parametrized using a 2-component (AGN+galaxy) model fit, we derived dust-corrected rest-frame magnitudes, colors, stellar masses and star formation rates (SFRs). We find that AGN hosts span a large range of stellar masses and SFRs. No color-bimodality is seen at any redshift in the AGN hosts, which are found to be mainly massive, red galaxies. Once accounting for the color-mass degeneracy in well defined mass-matched samples, we find a residual marginal enhancement of AGN incidence in redder galaxies with lower specific star formation rates, and we argue that this result might emerge because of our ability to properly account for AGN light contamination and dust extinction. Interestingly, we find that the probability for a galaxy to host a black hole growing at any given "specific accretion rate" (i.e. the ratio of X-ray luminosity to the host stellar mass) is almost independent of the host galaxy mass, while it decreases as a power-law with Lx/M. By analyzing the normalization of such probability distribution, we show how the incidence of AGN increases with redshift as rapidly as (1+z)^4, in close resemblance with the overall evolution of the specific star formation rate of the entire galaxy population. Although AGN activity and star formation in galaxies do appear to have a common triggering mechanism, at least in a statistical sense, within the COSMOS sample we do not find strong evidence of any 'smoking gun' signaling powerful AGN influence on the star-forming properties of their hosts galaxies.

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arXiv2012

Comparison of star formation rates from Halpha and infrared luminosities as seen by Herschel

We empirically test the relation between the SFR(LIR) derived from the infrared luminosity, LIR, and the SFR(Ha) derived from the Ha emission line luminosity using simple conversion relations. We use a sample of 474 galaxies at z = 0.06 - 0.46 with both Ha detection (from 20k zCOSMOS survey) and new far-IR Herschel data (100 and 160 μm). We derive SFR(Ha) from the Ha extinction corrected emission line luminosity. We find a very clear trend between E(B - V) and LIR that allows to estimate extinction values for each galaxy even if the Ha emission line measurement is not reliable. We calculate the LIR by integrating from 8 up to 1000 μm the SED that is best fitting our data. We compare SFR(Ha) with the SFR(LIR). We find a very good agreement between the two SFR estimates, with a slope of m = 1.01 \pm 0.03 in the SFR(LIR) vs SFR(Ha) diagram, a normalization constant of a = -0.08 \pm 0.03 and a dispersion of sigma = 0.28 dex.We study the effect of some intrinsic properties of the galaxies in the SFR(LIR)-SFR(Ha) relation, such as the redshift, the mass, the SSFR or the metallicity. The metallicity is the parameter that affects most the SFR comparison. The mean ratio of the two SFR estimators log[SFR(LIR)/SFR(Ha)] varies by approx. 0.6 dex from metal-poor to metal-rich galaxies (8.1 < log(O/H) + 12 < 9.2). This effect is consistent with the prediction of a theoretical model for the dust evolution in spiral galaxies. Considering different morphological types, we find a very good agreement between the two SFR indicators for the Sa, Sb and Sc morphologically classified galaxies, both in slope and normalization. For the Sd, irregular sample (Sd/Irr), the formal best-fit slope becomes much steeper (m = 1.62 \pm 0.43), but it is still consistent with 1 at the 1.5 sigma level, because of the reduced statistics of this sub-sample.

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arXiv2012

Deep observations of CO line emission from star-forming galaxies in a cluster candidate at z=1.5

We report results from a deep Jansky Very Large Array (JVLA) search for CO 1-0 line emission from galaxies in a candidate galaxy cluster at z~1.55 in the COSMOS field. We target 4 galaxies with optical spectroscopic redshifts in the range z=1.47-1.59. Two of these 4 galaxies, ID51613 and ID51813, are nominally detected in CO line emission at the 3-4 sigma level. We find CO luminosities of 2.4x10^10 K km/s pc^2 and 1.3x10^10 K km/s pc^2, respectively. Taking advantage from the clustering and 2-GHz bandwidth of the JVLA, we perform a search for emission lines in the proximity of optical sources within the field of view of our observations. We limit our search to galaxies with K<23.5 (AB) and z_phot=1.2-1.8. We find 2 bright optical galaxies to be associated with significant emission line peaks (>4 sigma) in the data cube, which we identify with the CO line emission. To test the reliability of the line peaks found, we performed a parallel search for line peaks using a Bayesian inference method. Monte Carlo simulations show that such associations are statistically significant, with probabilities of chance association of 3.5% and 10.7% for ID 51207 and ID 51380, respectively. Modeling of their optical/IR SEDs indicates that the CO detected galaxies and candidates have stellar masses and SFRs in the range (0.3-1.1)x10^11 M_sun and 60-160 M_sun/yr, with SFEs comparable to that found in other star-forming galaxies at similar redshifts. By comparing the space density of CO emitters derived from our observations with the space density derived from previous CO detections at z~1.5, and with semi-analytic predictions for the CO luminosity function, we suggest that the latter tend to underestimate the number of CO galaxies detected at high-redshift. Finally, we argue about the benefits of future blind CO searches in clustered fields with upcoming submm/radio facilities.

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arXiv2012

Evidence of strong quasar feedback in the early Universe

Most theoretical models invoke quasar driven outflows to quench star formation in massive galaxies, this feedback mechanism is required to account for the population of old and passive galaxies observed in the local universe. The discovery of massive, old and passive galaxies at z=2, implies that such quasar feedback onto the host galaxy must have been at work very early on, close to the reionization epoch. We have observed the [CII]158um transition in SDSSJ114816.64+525150.3 that, at z=6.4189, is one of the most distant quasars known. We detect broad wings of the line tracing a quasar-driven massive outflow. This is the most distant massive outflow ever detected and is likely tracing the long sought quasar feedback, already at work in the early Universe. The outflow is marginally resolved on scales of about 16 kpc, implying that the outflow can really affect the whole galaxy, as required by quasar feedback models. The inferred outflow rate, dM/dt > 3500 Msun/yr, is the highest ever found. At this rate the outflow can clean the gas in the host galaxy, and therefore quench star formation, in a few million years.

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arXiv2012

Herschel-PACS Observations of Far-IR CO Line Emission in NGC 1068: Highly Excited Molecular Gas in the Circumnuclear Disk

We report the detection of far-IR CO rotational emission from the prototypical Seyfert 2 galaxy NGC 1068. Using Herschel-PACS, we have detected 11 transitions in the J_upper=14-30 (E_upper/k_B = 580-2565 K) range, all of which are consistent with arising from within the central 10" (700 pc). The detected transitions are modeled as arising from 2 different components: a moderate excitation (ME) component close to the galaxy systemic velocity, and a high excitation (HE) component that is blueshifted by ~80 km s^{-1}. We employ a large velocity gradient (LVG) model and derive n_H2~10^{5.6} cm^{-3}, T_kin~170 K, and M_H2~10^{6.7} M_sun for the ME component, and n_H2~10^{6.4} cm^{-3}, T_kin~570 K, and M_H2~10^{5.6} M_sun for the HE component, although for both components the uncertainties in the density and mass are plus/minus (0.6-0.9) dex. We compare the CO line profiles with those of other molecular tracers observed at higher spatial and spectral resolution, and find that the ME transitions are consistent with these lines arising in the ~200 pc diameter ring of material traced by H_2 1-0 S(1) observations. The blueshift of the HE lines may also be consistent with the bluest regions of this H_2 ring, but a better kinematic match is found with a clump of infalling gas ~40 pc north of the AGN. We discuss the prospects of placing the HE component near the AGN, and conclude that while the moderate thermal pressure precludes an association with the ~1 pc radius H_2O maser disk, the HE component could potentially be located only a few parsecs more distant from the AGN, and might then provide the N_H~10^{25} cm^{-2} column obscuring the nuclear hard X-rays. Finally, we also report sensitive upper limits extending up to J_upper=50, which place constraints on a previous model prediction for the CO emission from the X-ray obscuring torus. [Abridged]

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arXiv2012

Bolometric luminosities and Eddington ratios of X-ray selected Active Galactic Nuclei in the XMM-COSMOS survey

Bolometric luminosities and Eddington ratios of both X-ray selected broad-line (Type-1) and narrow-line (Type-2) AGN from the XMM-Newton survey in the COSMOS field are presented. The sample is composed by 929 AGN (382 Type-1 AGN and 547 Type-2 AGN) and it covers a wide range of redshifts, X-ray luminosities and absorbing column densities. About 65% of the sources are spectroscopically identified as either Type-1 or Type-2 AGN (83% and 52% respectively), while accurate photometric redshifts are available for the rest of the sample. The study of such a large sample of X-ray selected AGN with a high quality multi-wavelength coverage from the far-infrared (now with the inclusion of Herschel data at 100 micron and 160 micron) to the optical-UV allows us to obtain accurate estimates of bolometric luminosities, bolometric corrections and Eddington ratios. The kbol-Lbol relations derived in the present work are calibrated for the first time against a sizable AGN sample, and rely on observed redshifts, X-ray luminosities and column density distributions. We find that kbol is significantly lower at high Lbol with respect to previous estimates by Marconi et al. (2004) and Hopkins et al. (2007). Black hole masses and Eddington ratios are available for 170 Type-1 AGN, while black hole masses for Type-2 AGN are computed for 481 objects using the black hole mass-stellar mass relation and the morphological information. We confirm a trend between kbol and lambda_Edd, with lower hard X-ray bolometric corrections at lower Eddington ratios for both Type-1 and Type-2 AGN. We find that, on average, Eddington ratio increases with redshift for all Types of AGN at any given Mbh, while no clear evolution with redshift is seen at any given Lbol.

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arXiv2012

A survey of molecular gas in luminous sub-millimetre galaxies

We present the results from a survey for 12CO emission in 40 luminous sub-millimetre galaxies (SMGs), with 850um fluxes of S850 = 4 - 20 mJy, conducted with the Plateau de Bure Interferometer. We detect 12CO emission in 32 SMGs at z~1.2 - 4.1, including 16 SMGs not previously published. Using multiple 12CO line (J_up =2 - 7) observations, we derive a median spectral line energy distribution for luminous SMGs and use this to estimate a mean gas mass of (5.3 +/- 1.0) \times 10^10 Msun. We report the discovery of a fundamental relationship between 12CO FWHM and 12CO line luminosity in high-redshift starbursts, which we interpret as a natural consequence of the baryon-dominated dynamics within the regions probed by our observations. We use far-infrared luminosities to assess the star-formation efficiency in our SMGs, finding a steepening of the L'CO-LFIR relation as a function of increasing 12CO J_up transition. We derive dynamical masses and molecular gas masses, and use these to determine the redshift evolution of the gas content of SMGs, finding that they do not appear to be significantly more gas rich than less vigorously star-forming galaxies at high redshifts. Finally, we collate X-ray observations, and study the interdependence of gas and dynamical properties of SMGs with their AGN activity and supermassive black hole masses (MBH), finding that SMGs lie significantly below the local M_BH-sigma relation. We conclude that SMGs represent a class of massive, gas-rich ultraluminous galaxies with somewhat heterogeneous properties, ranging from starbursting disc-like systems with L~10^12 L_sun, to the most highly star-forming mergers in the Universe.

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arXiv2012

The AGN content in luminous IR galaxies at z\sim2 from a global SED analysis including Herschel data

We use Herschel-PACS far-infrared data, combined with previous multi-band information and mid-IR spectra, to properly account for the presence of an active nucleus and constrain its energetic contribution in luminous infrared (IR) sources at z\sim2. The sample is composed of 24 sources in the GOODS-South field, with typical IR luminosity of 10^{12} Lo. Data from the 4 Ms Chandra X-ray imaging in this field are also used to identify and characterize AGN emission. We reproduce the observed spectral energy distribution (SED), decomposed into a host-galaxy and an AGN component. A smooth-torus model for circum-nuclear dust is used to account for the direct and re-processed contribution from the AGN. We confirm that galaxies with typical L_{8-1000um}\sim10^{12}Lo at z\sim2 are powered predominantly by star-formation. An AGN component is present in nine objects (\sim35% of the sample) at the 3sigma confidence level, but its contribution to the 8-1000 um emission accounts for only \sim5% of the energy budget. The AGN contribution rises to \sim23% over the 5-30 um range (in agreement with Spitzer IRS results) and to \sim60% over the narrow 2-6 um range. The presence of an AGN is confirmed by X-ray data for 3 (out of nine) sources, with X-ray spectral analysis indicating the presence of significant absorption, i.e. NH\sim10^{23}-10^{24} cm^{-2}. An additional source shows indications of obscured AGN emission from X-ray data. The comparison between the mid-IR--derived X-ray luminosities and those obtained from X-ray data suggests that obscuration is likely present also in the remaining six sources that harbour an AGN according to the SED-fitting analysis.

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arXiv2012

Physical properties of Lyman-alpha emitters at $z\sim 0.3$ from UV-to-FIR measurements

The analysis of the physical properties of low-redshift Ly$α$ emitters (LAEs) can provide clues in the study of their high-redshift analogues. At $z \sim 0.3$, LAEs are bright enough to be detected over almost the entire electromagnetic spectrum and it is possible to carry out a more precise and complete study than at higher redshifts. In this study, we examine the UV and IR emission, dust attenuation, SFR and morphology of a sample of 23 GALEX-discovered star-forming (SF) LAEs at $z \sim 0.3$ with direct UV (GALEX), optical (ACS) and FIR (PACS and MIPS) data. Using the same UV and IR limiting luminosities, we find that LAEs at $z\sim 0.3$ tend to be less dusty, have slightly higher total SFRs, have bluer UV continuum slopes, and are much smaller than other galaxies that do not exhibit Ly$α$ emission in their spectrum (non-LAEs). These results suggest that at $z \sim 0.3$ Ly$α$ photons tend to escape from small galaxies with low dust attenuation. Regarding their morphology, LAEs belong to Irr/merger classes, unlike non-LAEs. Size and morphology represent the most noticeable difference between LAEs and non-LAEs at $z \sim 0.3$. Furthermore, the comparison of our results with those obtained at higher redshifts indicates that either the Ly$α$ technique picks up different kind of galaxies at different redshifts or that the physical properties of LAEs are evolving with redshift.

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arXiv2012

Enhanced star formation rates in AGN hosts with respect to inactive galaxies from PEP-Herschel observations

We compare the average star formation (SF) activity in X-ray selected AGN hosts with mass-matched control inactive galaxies,including star forming and quiescent sources, at 0.5 10sigma) for bright AGNs. However, when comparing to star forming galaxies only, AGN hosts are broadly consistent with the locus of their `main sequence'. We investigate the relative far-IR luminosity distributions of active and inactive galaxies, and find a higher fraction of PACS detected, hence normal and highly star forming systems among AGN hosts. Although different interpretations are possible, we explain our findings as a consequence of a twofold AGN growth path: faint AGNs evolve through secular processes, with instantaneous AGN accretion not tightly linked to the current total SF in the host, while luminous AGNs co-evolve with their hosts through periods of enhanced AGN activity and SF, possibly through major mergers. While an increased SF with respect to non-AGNs of similar mass is expected in the latter, we interpret the modest SF offsets measured in low-Lx AGN hosts as either a) generated by non-synchronous accretion and SF histories in a merger scenario or b) due to possible connections between instantaneous SF and accretion that can be induced by smaller scale (non-major merger) mechanisms. Far-IR luminosity distributions favour the latter scenario.

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