Delphine Marcillac

Spitzer Mid- to Far-Infrared Flux Densities of Distant Galaxies

We study the infrared (IR) properties of high-redshift galaxies using deep Spitzer 24, 70, and 160 μm data. Our primary interest is to improve the constraints on the total IR luminosities, L_(IR), of these galaxies. We combine the Spitzer data in the southern Extended Chandra Deep Field with a K_s-band-selected galaxy sample and photometric redshifts from the Multiwavelength Survey by Yale-Chile. We used a stacking analysis to measure the average 70 and 160 μm flux densities of 1.5 250 μJy and 1.5 250 μJy have S_(70)/S_(24) flux ratios comparable to sources with X-ray detections or red rest-frame IR colors, suggesting that warm dust possibly heated by AGNs may contribute to the high 24 μm emission. Based on the average 24-160 μm flux densities, nearly all 24 μm-selected galaxies at 1.5 6 × 10^(12) L_⊙ are quite rare, with a surface density ~30 ± 10 deg^(-2), corresponding to ~2 ± 1 × 10^(-6) Mpc^(-3) over 1.5 < z < 2.5.

The strong transformation of spiral galaxies infalling into massive clusters at z≈ 0.2

We describe two peculiar galaxies falling into the massive galaxy clusters Abell 1689 (Z ≈ 0.18) and Abell 2667 (Z ≈0.23), respectively. Hubble Space Telescope (HST) images show extraordinary trails composed of bright blue knots (-16.5 < M < -11.5 mag) and stellar streams associated with each of these systems. Combining optical, near- and mid-infrared and radio observations we prove that while both galaxies show similar extended trails of star-forming knots, their recent star formation histories are different. One (≈L*) is experiencing a strong burst of star formation, appearing as a rare example of a luminous infrared cluster galaxy. In comparison, the other (≈0.1L*) has recently ceased its star formation activity. Our model suggests that the morphologies and star formation in these galaxies have been influenced by the combined action of tidal interaction (likely with the cluster potential) and of ram pressure with the intracluster medium (ICM). These results can be used to gain more insights to the origin of SOs, dwarf and ultracompact dwarf (UCD) cluster galaxies.

Mid-infrared spectroscopy of lensed galaxies at 1 < z < 3: The nature of sources near the mips confusion limit

We present Spitzer IRS mid-infrared spectra for 15 gravitationally lensed, 24 μm-selected galaxies, and combine the results with four additional very faint galaxies with IRS spectra in the literature. The median intrinsic 24 μm flux density of the sample is 130 μJy, enabling a systematic survey of the spectral properties of the very faint 24 μm sources that dominate the number counts of Spitzer cosmological surveys. Six of the 19 galaxy spectra (32%) show the strong mid-IR continuua expected of AGNs; X-ray detections confirm the presence of AGNs in three of these cases, and reveal AGNs in two other galaxies. These results suggest that nuclear accretion may contribute more flux to faint 24 μm-selected samples than previously assumed. Almost all the spectra show some aromatic (PAH) emission features; the measured aromatic flux ratios do not show evolution from z = 0. In particular, the high signal-to-noise mid-IR spectrum of SMM J163554.2+661225 agrees remarkably well with low-redshift, lower luminosity templates. We compare the rest-frame 8 μm and total infrared luminosities of star-forming galaxies, and find that the behavior of this ratio with total IR luminosity has evolved modestly from z = 2 to z = 0. Since the high aromatic-to-continuum flux ratios in these galaxies rule out a dominant contribution by AGNs, this finding implies systematic evolution in the structure and/or metallicity of infrared sources with redshift. It also has implications for the estimates of star-forming rates inferred from 24 μm measurements, in the sense that at z ~ 2, a given observed frame 24 μm luminosity corresponds to a lower bolometric luminosity than would be inferred from low-redshift templates of similar luminosity at the corresponding rest wavelength.

IR Observations of MS 1054–03: Star Formation and Its Evolution in Rich Galaxy Clusters

We study the IR properties of galaxies in the cluster MS 1054-03 at z = 0.83 by combining MIPS 24 μm data with spectra of more than 400 galaxies and a very deep K-band-selected catalog. Nineteen IR cluster members are selected spectroscopically, and an additional 15 are selected by their photometric redshifts. We derive the IR luminosity function of the cluster and find strong evolution compared to the similar-mass Coma Cluster. The best-fitting Schechter function gives L = 11.49 L☉ with a fixed faint-end slope, about 1 order of magnitude larger than that in Coma. The rate of evolution of the IR luminosity from Coma to MS 1054-03 is consistent with that found in field galaxies, and it suggests that some internal mechanism, e.g., the consumption of the gas fuel, is responsible for the general decline of the cosmic SFR in different environments. The mass-normalized integrated SFR within 0.5R200 in MS 1054-03 also shows evolution compared with other rich clusters at lower redshifts, but the trend is less conclusive if the mass selection effect is considered. A nonnegligible fraction (13% ± 3%) of cluster members are forming stars actively, and the overdensity of IR galaxies is about 20 compared to the field. It is unlikely that clusters only passively accrete star-forming galaxies from the surrounding fields and have their star formation quenched quickly afterward; instead, many cluster galaxies still have large amounts of gas, and their star formation may be enhanced by the interaction with the cluster.

Strong dusty bursts of star formation in galaxies falling into the cluster RX J0152.7-1357

We have observed the cluster RX J0152.7-1357 (z ~ 0.83) at 24 μm with the Multiband Imaging Photometer for Spitzer (MIPS). We detected 22 sources associated with spectroscopically confirmed cluster members, while 10 more have photometric redshifts compatible with membership. Two of the 32 likely cluster members contain obvious active nuclei, while the others are associated with dusty star formation. The median IR-determined star formation rate among the remaining galaxies is estimated at 22 M☉ yr-1, significantly higher than in previous estimates from optical data. Most of the mid-infrared (MIR) emitting galaxies also have optical emission lines, but a few do not and hence have completely hidden bursts of star formation or AGN activity. An excess of MIR-emitting galaxies is seen in the cluster, compared to the field at the same redshift. The MIR cluster members are more associated with previously detected infalling late-type galaxies rather than triggered by the ongoing merging of bigger X-ray clumps. Rough estimates also show that ram pressure may not be capable of stripping the gas away from cluster outskirt galaxies, but it may disturb the gas enough to trigger the star formation activity. Harassment can also play a role if, for example, these galaxies belong to poor galaxy groups. Thus, bursts of star formation occur in the cluster environment and could also help consume the galaxy gas content, in addition to ram pressure, harassment, or galaxy-galaxy strong interactions.

The ultraviolet properties of luminous infrared galaxies at z ~ 0.7 - Is there any evolution in their dust attenuation?

Aims. The total infrared (TIR: 8-1000 � m) and far-ultraviolet (FUV:∼ 1500A) luminosity functions of galaxies and the related luminosity densitiesρT IR andρFUV are known to evolve with redshift from z=0 to z∼1 but with a different rate: the galaxy populations appear brighter in the past at both wavelengths but the evolution in TIR is larger than in FUV. It leads to an increase of the ratio of TIR to FUV luminosity densitiesρT IR/ρFUV which can be interpreted as a global increase of the dust attenuation from z=0 to z∼1. Our aim is to understand the origin of this increase: is it ent irely due to a variation of the dust attenuation with the lumi nosity of the galaxies as seen as z=0 or are properties of galaxies evolving with the redshift? Methods. We focus on infrared galaxies more luminous than LTIR = 10 11 L⊙ at z∼0.7 observed by SPITZER/MIPS and we measure their ultraviolet emission at 2310 A from GALEX images. These Luminous InfraRed Galaxies (LIRGs) represent the bulk of the TIR luminosity density at intermediate redshift. The analysis of the ratio of TIR to FUV (rest-frame) luminosity (LTIR/LFUV) enables us to discuss their dust attenuation and to compare it to what is found in the nearby universe for galaxies of similar infrared l uminosity and selected in the same way Results. Some evolution of LTIR/LFUV and therefore of dust attenuation is found: LIRGs at z=0.7 span a larger range of LTIR/LFUV ratios than at z=0 and their mean dust attenuation at FUV wavelengths is found∼0.5 mag lower than for their local counterparts. The decrease of dust attenuation is found lower than that reported in other studies for bright galaxies selected in UV res t-frame at z=1 and 2. A semi-quantitative analysis is performed which accounts for the general increase of dust attenuation with the bolometric luminosity of galaxies: it is found that the slight decrease of dust attenuation for LIRGs at z=0.7 remains consistent with the increase ofρT IR/ρFUV with redshift.

SPITZER OBSERVATIONS OF COLD DUST GALAXIES

We combine new Spitzer Space Telescope observations in the mid-infrared and far-infrared (FIR) with SCUBA 850 μm observations to improve the measurement of dust temperatures, masses, and luminosities for 11 galaxies of the SCUBA Local Universe Galaxy Survey. By fitting dust models we measure typical dust masses of 107.9 M ☉ and dust luminosities of ~1010 L ☉, for galaxies with modest star formation rates. The data presented in this paper combined with previous observations show that cold dust is present in all types of spiral galaxies and is a major contributor to their total luminosity. Because of the lower dust temperature of the SCUBA sources measured in this paper, they have flatter FIR νFν(160 μm)/νFν(850 μm) slopes than the larger Spitzer Infrared Nearby Galaxies Survey (SINGS), the sample that provides the best measurements of the dust properties of galaxies in the nearby universe. The new data presented here added to SINGS extend the parameter space that is well covered by local galaxies, providing a comprehensive set of templates that can be used to interpret the observations of nearby and distant galaxies.

Hubble Ultra Deep Field-JD2: Mid-Infrared Evidence for a z ~ 2 Luminous Infrared Galaxy

The Hubble Ultra Deep Field source JD2 presented in Mobasher et al. is an unusual galaxy that is very faint at all wavelengths shortward of 1.1 μm. Photometric redshift fits to data between 0.4 and 8 μm yield a significant probability that it is an extremely massive galaxy at z ~ 6.5. In this paper we present new photometry at 16 and 22 μm from Spitzer Infrared Spectrograph (IRS) peak-up imaging of the Great Observatories Origins Deep Survey (GOODS) fields. We find that the spectral energy distribution shows a factor of ~4 rise in flux density between the 16 and 22 μm bandpass, which is most likely due to the entrance of polycyclic aromatic hydrocarbon emission features into the 22 and 24 μm passbands. The flux ratio between these bandpasses can be best fit by a z = 1.7 luminous infrared galaxy with a bolometric luminosity of (2-6) × 10^(11) L_⊙ corresponding to a star formation rate of 80 M_⊙ yr^(-1). The predicted flux density values at other longer wavelengths are below the detection limits of current instrumentation, but such sources could potentially be detected in lensed submillimeter surveys. Reevaluation of the optical/near-infrared photometry continues to favor z > 6 photometric redshift solutions, but we argue that the consistency of the multiwavelength parameters of this galaxy with other dusty starbursts favor the z ~ 2 mid-infrared photometric redshift. The data presented here provide evidence that optically undetected near-infrared sources that are detected at 24 μm are most likely dusty, starburst galaxies at a redshift of z ~ 2 with stellar masses >10^(10) M_⊙.

The Environment on a Few Mpc Scales of Infrared Luminous Galaxies at Redshift z~1

We investigate the environment of infrared-luminous galaxies [ -->LIR(8–1000 μ m) > 1011 L☉]. We focus on the redshift range -->0.7 ≤ z≤ 1, where these galaxies dominate the star formation activity and play a significant role in galaxy evolution. We employ MIPS 24 μm data to identify infrared galaxies in the Extended Groth Strip (EGS). We use a local density indicator to probe the environment on a few Mpc scales and a group member catalog, both of which make use of the DEEP2 spectroscopic redshift catalog, to quantify the environment of these galaxies. We find that the local environment of LIRGs and ULIRGs is intermediate between that of blue and red galaxies. LIRGs and ULIRGs avoid underdense environments and inhabit local environments that are more dense on average than those of other DEEP2 galaxies at similar redshifts. However, when the comparison sample of the non-IR DEEP2 galaxies is restricted to have the same range of stellar mass, color, or luminosity as the IR galaxies, there is no longer any significant difference in environment: the IR galaxies follow the same trends in the color-environment and luminosity-environment relations observed at -->z ~ 1. We also find that about 30% of the LIRGs and ULIRGs belong to groups, associated with a minimum dark matter halo of -->6 × 1012 M☉ h−1. The group members constitute 20% of the sources responsible for the IR star formation rate density and comoving energy density at -->z ~ 1.

The Strong Transformation of Spiral Galaxies Infalling into Massive Clusters at z~ 0.2

We report the discovery of two peculiar galaxies infalling into the lensing clusters of galaxies Abell 1689 (z∼0.18) and 2667 (z∼0.23). Hubble Space Telescope images show extraordinary trails composed by blue bright knots and stellar streams associated with both these systems, an ∼L ∗ and ∼0.1L ∗ galaxy. Under the combined action of tidal interaction with the cluster potential and of ram pressure by the intra-cluster medium the morphologies and star formation histories of these two galaxies are strongly perturbed. While in the massive system tidal interactions are the dominant effect and are able to produce a sinking of gas towards the galaxy center triggering a strong burst of star formation and changing galaxy’s morphology, in the smaller galaxy the effects of gravitation are reduced by ram pressure stripping which blows away the neutral hydrogen from the galactic disk, quenching the star formation activity and transforming a gas rich late type spiral into quiescent disk dominated early type system.This result is a new additional evidence that galaxy mass represents the main driver of galaxy evolution, even during their dive into the harsh cluster environment and can give additional insights on the origin of S0s and dwarf cluster galaxies.