arXiv subjects

Paul P. van der Werf

Publications and source records attributed to Paul P. van der Werf.

72 records · Page 4Linked to original sources

arXiv2011

Genesis of the dusty Universe: modeling submillimetre source counts

We model the evolution of IR galaxies using a phenomenological approach to match the observed source counts at different IR wavelengths. We introduce a new algorithm for reproducing source counts based on direct integration of probability distributions rather than Monte-Carlo sampling. We construct a simple model for the evolution of the luminosity function and the colour distribution of IR galaxies which utilizes a minimum number of free parameters. Moreover we analyze how each of these parameters is constrained by observational data. The model is based on pure luminosity evolution and adopts the Dale & Helou SED templates. We find that the 850um source counts and their redshift distribution depend strongly on the shape of the luminosity evolution function, but only weakly on the details of the SEDs. We derive the best-fit evolutionary model using the 850um counts and redshift distribution as constraints. Moreover our best-fit shows a flattening of the faint end of the luminosity function towards high redshifts and requires a colour evolution which implies the typical dust temperatures of objects with the same luminosities to decrease with redshift. We compare our best-fit model to observed source counts at shorter and longer wavelengths which indicates our model reproduces the 70um and 1100um source counts remarkably well, but under-produces the counts at intermediate wavelengths. Analysis reveals that the discrepancy arises at low redshifts, indicating that revision of the adopted SED library towards lower dust temperatures (at a fixed infrared luminosity) is required. This modification is equivalent to a population of cold galaxies existing at low redshifts, as also indicated by recent Herschel results, which are underrepresented in IRAS sample. We show that the modified model successfully reproduces the source counts in a wide range of IR and submm wavelengths.

astro-ph.CO↗

arXiv2007

The Origin of Line Emission in Massive z~2.3 Galaxies: Evidence for Cosmic Downsizing of AGN Host Galaxies

Using the Gemini Near-InfraRed Spectrograph (GNIRS), we have assembled a complete sample of 20 K-selected galaxies at 2.0<z<2.7 with high quality near-infrared spectra. As described in a previous paper, 9 of these 20 galaxies have strongly suppressed star formation and no detected emission lines. The present paper concerns the 11 galaxies with detected Halpha emission, and studies the origin of the line emission using the GNIRS spectra and follow-up observations with SINFONI on the VLT. Based on their [NII]/Halpha ratios, the spatial extent of the line emission and several other diagnostics, we infer that four of the eleven emission-line galaxies host narrow line active galactic nuclei (AGNs). The AGN host galaxies have stellar populations ranging from evolved to star-forming. Combining our sample with a UV-selected galaxy sample at the same redshift that spans a broader range in stellar mass, we find that black-hole accretion is more effective at the high-mass end of the galaxy distribution (~2.9x10^11 Msun) at z~2.3. Furthermore, by comparing our results with SDSS data, we show that the AGN activity in massive galaxies has decreased significantly between z~2.3 and z~0. AGNs with similar normalized accretion rates as those detected in our K-selected galaxies reside in less massive galaxies (~4.0x10^10 Msun) at low redshift. This is direct evidence for downsizing of AGN host galaxies. Finally, we speculate that the typical stellar mass-scale of the actively accreting AGN host galaxies, both at low and at high redshift, might be similar to the mass-scale at which star-forming galaxies seem to transform into red, passive systems.

astro-ph↗

arXiv2007

Mid-infrared diagnostics of starburst galaxies: clumpy, dense structures in star-forming regions in the Antennae (NGC 4038/4039)

Recently, mid-infrared instruments have become available on several large ground-based telescopes, resulting in data sets with unprecedented spatial resolution at these long wavelengths. In this paper we examine 'ground-based-only' diagnostics, which can be used in the study of star-forming regions in starburst galaxies. By combining output from the stellar population synthesis code Starburst 99 with the photoionization code Mappings, we model stellar clusters and their surrounding interstellar medium, focusing on the evolution of emission lines in the N- and Q-band atmospheric windows (8-13 and 16.5-24.5 micron respectively) and those in the near-infrared. We address the detailed sensitivity of various emission line diagnostics to stellar population age, metallicity, nebular density, and ionization parameter. Using our model results, we analyze observations of two stellar clusters in the overlap region of the Antennae galaxies obtained with VLT Imager and Spectrometer for mid Infrared (VISIR). We find evidence for clumpy, high density, ionized gas. The two clusters are young (younger than 2.5 and 3 Myr respectively), the surrounding interstellar matter is dense (10^4 cm^-3 or larger) and can be characterized by a high ionization parameter (logU > -1.53). Detailed analysis of the mid-infrared spectral features shows that a (near-)homogeneous medium cannot account for the observations, and that complex structure on scales below the resolution limit, containing several young stellar clusters embedded in clumpy gas, is more likely.

astro-ph↗

arXiv2007

First CO J=6-5, 4-3 detections in local ULIRGs: the dense gas in Mrk231, and its colling budget

We report on detections of the high-excitation CO J=6-5, J=4-3 lines in Mrk231, a prototypical Ultra Luminous Infrared Galaxy (ULIRG) and Seyfert 1 QSO. These observations are combined with CO J=3-2, HCN J=4-3 (this work), and CO J=2-1, J=1-0, 13CO J=2-1, HCN J=1-0 measurements taken from the literature to provide better constraints on the properties of the molecular gas in an extreme starburst/QSO in the local Universe. We find that the CO J=4-3 and J=6-5 transitions trace a different gas phase from that dominating the lower three CO transitions, with n(H_2) ~ (1-3)x10^4 cm-3 and Tk ~ (40-70) K. This phase is responsible for the luminous HCN emission, and contains most of the H2 gas mass of this galaxy. The total CO line cooling emanating from this dense phase is found similar to that of the [CII] line at 158 micron, suggesting a very different thermal balance to that seen in lower IR-luminosity galaxies, and one likely dominated by dense photon-dominated regions. Our dense "sampling" of the CO rotational ladder and the HCN lines enables us to produce well-constrained Spectral Line Energy Distributions (SLEDs) for the dense molecular gas in Mrk231 and compare them to those of high redshift starbursts, many of which have SLEDs that may be affected by strong lensing. Finally, we use our local molecular line excitation template to assess the capabilities of future cm and mm/sub-mm arrays in detecting CO and HCN transitions in similar systems throughout the local and distant universe.

astro-ph↗

arXiv2006

Subarcsecond Resolution Mid-Infrared Observations of Super Star Clusters in the Antennae (NGC4038/4039)

In this letter we present ground-based subarcsecond mid-infrared imaging and spectroscopy of young super star clusters in the overlap region of the merging galaxies NGC4038/4039 (the Antennae) obtained with the VLT Imager and Spectrometer for mid-Infrared (VISIR). With its unprecedented spatial resolution VISIR begins to resolve the HII/PDR complexes around the star-forming regions for the first time. In the N-band spectra of two young star clusters unexpectedly low polycyclic aromatic hydrocarbon (PAH) emission is observed, compared to what is seen with the Infrared Space Observatory (ISO) and with the Spitzer Space Telescope. We conclude that a large fraction of the PAH emission cannot directly be associated with the super star clusters, but originate from an extended region of at least 215 pc radius around the clusters. In the distribution of [NeII] 12.81 micron emission a highly obscured cluster is discovered that does not have an optical or near-infrared counterpart.

astro-ph↗

arXiv2006

Extreme superstarclusters

The presence of superstarclusters is a characteristic feature of starburst galaxies. We examine the properties of star forming regions and young star clusters in various environments, ranging from common to extreme. We then discuss new high spatial resolution mid-infrared imaging and spectroscopy of extreme superstarclusters in the obscured region of the Antennae (NGC4038-4039). We find that the PAH emission in this region is not dominated by the superstarclusters but is mostly diffuse. Emission line ratios found in our high spatial resolution data differ significantly from those in larger apertures, strongly affecting the derived results.

astro-ph↗

arXiv2004

Dissecting starburst galaxies with infrared observations

The infrared regime contains a number of unique diagnostic features for probing the astrophysics of starburst galaxies. After a brief summary of the most important tracers, we focus in detail on the use of emission lines to probe the upper part of the main sequence in a young superstarcluster in the Antennae, and the compact, dusty starburst in the nucleus of the nearby ultraluminous infrared galaxy Arp220

astro-ph↗

arXiv2004

Multiply-imaged submm galaxy in a z~2.5 group

We present observations of a remarkable submillimetre-selected galaxy, SMMJ16359+6612. This distant galaxy lies behind the core of a massive cluster of galaxies, A2218, and is gravitationally lensed by the foreground cluster into three discrete images which were identified in deep submillimetre maps of the cluster core at both 450 and 850micron. Subsequent follow-up using deep optical and NIR images identify a faint counterpart to each of the 3 images, with similar red optical--NIR colours and HST morphologies. By exploiting a detailed mass model for the cluster lens we estimate that the combined images of this galaxy are magnified by a factor of ~45, implying that this galaxy would have un-lensed magnitudes K_s=22.9 and I=26.1, and an un-lensed 850micron flux density of only 0.8mJy. Moreover, the highly constrained lens model predicted the redshift of SMMJ16359+6612 to be z=2.6+/-0.4. We confirm this estimate using deep optical and NIR Keck spectroscopy, measuring a redshift of z=2.516. SMMJ16359+6612 is the faintest submm-selected galaxy so far identified with a precise redshift. Thanks to the large gravitational magnification of this source, we identify 3 sub-components in this submm galaxy, which are also seen in the NIRSPEC data, arguing for either a strong dust (lane) absorption or a merger. Interestingly, there are 2 other highly-amplified galaxies at almost identical redshifts in this field (although neither is a strong submm emitter). The 3 galaxies lie within a ~100kpc region on the background sky, suggesting this submm galaxy is located in a dense high-redshift group.

astro-ph↗

arXiv2001

Probing the evolution of galaxies using redshifted H-alpha emission

In this paper we review the present status and implications of H-alpha surveys at various redshifts. With the advent of sensitive wide-format near-infrared detectors on large telescopes, deep and extensive H-alpha surveys are now feasible to redshift z~2.5. The cosmic star formation history can therefore be traced out to this redshift using H-alpha alone, avoiding complications arising from the comparison of different tracers at different redshifts. The H-alpha surveys to date confirm the rapid increase in luminosity density from z=0 out to z=1, and show that this increase flattens off at higher redshifts, remaining approximately constant out to at least z~2.2. We also discuss the prospects for determining the masses of high redshift galaxies based on emission lines. A set of high-quality H-alpha rotation curves of samples of disk galaxies at a number of different redshifts would allow a study of the evolution of the Tully-Fisher relation and address fundamental issues in disk galaxy formation. Such a program remains challenging even with present-day large telescopes.

astro-ph↗

arXiv2001

Starbursts in ultraluminous infrared galaxies - fueling and properties

The properties of starbursts in ultraluminous infrared galaxies are discussed, with particular emphasis on the fueling, the amount of extinction and the intrinsic properties of the nuclear starbursts. It is shown by the example of NGC6240 that the H_2 vibrational lines can be used to measure the rate of gas inflow into the potential well, which is sufficient to fuel a nuclear starburst of the intensity required to account for the far-infrared emission. It is shown that in Arp220 the faintness of all tracers of ionized gas can be accounted for by Lyman continuum absorption by dust within the ionized regions, combined with significant (but not extreme) extinction; there is no reason to invoke the presence of extreme extinction, an old starburst, or an additional non-stellar power source in Arp220.

astro-ph↗

arXiv2001

Lessons from lensed Lyman break galaxies: can dusty Lyman break galaxies produce the submillimetre counts and background?

Can the submillimetre counts and background be produced by applying a locally derived extinction correction to the population of Lyman break galaxies? We investigate the submillimetre emission of two strongly lensed Lyman break galaxies (MS1512+36-cB58 and MS1358+62-G1) and find that the procedure that is used to predict the submillimetre emission of the Lyman break galaxy population overpredicts the observed 850 micron fluxes by a factor of up to 14. This result calls for caution in applying local correlations to distant galaxies. It also shows that large extinction corrections on Lyman break galaxies should be viewed with skepticism. It is concluded that the Lyman break galaxies may contribute to the submillimetre background at the 25 to 50% level. The brighter submillimetre galaxies making up the rest of the background are either not detected in optical surveys, or if they are detected, their submillimetre emission cannot be reliably estimated from their rest-frame ultraviolet properties.

astro-ph↗

arXiv2001

Can dusty Lyman break galaxies produce the submillimeter counts and background? Lessons from lensed Lyman break galaxies

Can the submillimeter counts and background be produced by applying a locally derived extinction correction to the population of Lyman break galaxies? We investigate the submillimeter emission of two strongly lensed Lyman break galaxies (MS1512+36-cB58 and MS1358+62-G1) and find that the procedure that is used to predict the submillimeter emission of the Lyman break galaxy population overpredicts the observed 850micron fluxes by up to a factor of 14. This result calls for caution in applying local correlations to distant galaxies. It also shows that large extinction corrections on Lyman break galaxies should be viewed with skepticism. It is concluded that the Lyman break galaxies may contribute to the submillimeter background at the 25 to 50% level. The brighter submillimeter galaxies making up the rest of the background are either not detected in optical surveys, or if they are detected, their submillimeter emission cannot be reliably estimated from their rest-frame ultraviolet properties.

astro-ph↗

arXiv2000

Halpha emitting galaxies and the cosmic star formation rate at z = 2.2

About 10 candidate Halpha emitting galaxies at z = 2.2 have been detected in a 2.1 um narrow band imaging survey covering an area of 100 sq. arcmin including the WFPC2 and STIS fields in the Hubble Deep Field South. Six of these have subsequently been confirmed spectroscopically using ISAAC at the ESO VLT. Star formation rates of the individual galaxies derived from their Halpha fluxes are 20-35 Msolar/yr, without any correction for extinction, whereas SFRs derived from their rest frame UV continuum fluxes are up to a factor of 4 lower - consistent with lower extinction to Halpha. Velocity dispersions are typically ~ 100km/s and one galaxy, observed under the most favorable conditions, shows a rotation curve with a terminal velocity ~ 140 km/s at ~ 3kpc radius which is within the range observed for nearby spiral galaxies. These thus appear to be relatively massive systems at high redshift. Comparison with the HST NICMOS grism Halpha survey of Yan et al. (1999) reveals little or no evolution in the Halpha luminosity function between z ~ 1.3 and 2.2. The inferred star formation rate density of 0.12 Msolar/Mpc^3/yr at z = 2.2 is also equal to that at z ~ 3-4.5 derived by Steidel et al.(1999) from extinction corrected UV continuum fluxes.

astro-ph↗

arXiv2000

H2 emission as a diagnostic of physical processes in starforming galaxies

Observations and interpretation of extragalactic rotational and rovibrational H2 emission are reviewed. Direct observations of H2 lines do not trace bulk H2 mass, but excitation rate. As such, the H2 lines are unique diagnostics, if the excitation mechanism can be determined, which generally requires high-quality spectroscopy and suitable additional data. The diagnostic power of the H2 lines is illustrated by two cases studies: H2 purely rotational line emission from the disk of the nearby spiral galaxy NGC891 and high resolution imaging and spectroscopy of H2 vibrational line emision from the luminous merger NGC6240.

astro-ph↗

arXiv1998

Discovery of distant high luminosity infrared galaxies

We have developed a method for selecting the most luminous galaxies detected by IRAS based on their extreme values of R, the ratio of 60 micron and B-band luminosity. These objects have optical counterparts that are close to or below the limits of Schmidt surveys. We have tested our method on a 1079 deg^2 region of sky, where we have selected a sample of IRAS sources with 60 micron flux densities greater than 0.2 Jy, corresponding to a redshift limit z~1 for objects with far-IR luminosities of 10^{13} L_sun. Optical identifications for these were obtained from the UK Schmidt Telescope plates, using the likelihood ratio method. Optical spectroscopy has been carried out to reliably identify and measure the redshifts of six objects with very faint optical counterparts, which are the only objects with R>100 in the sample. One object is a hyperluminous infrared galaxy (HyLIG) at z=0.834. Of the remaining, fainter objects, five are ultraluminous infrared galaxies (ULIGs) with a mean redshift of 0.45, higher than the highest known redshift of any non-hyperluminous ULIG prior to this study. High excitation lines reveal the presence of an active nucleus in the HyLIG, just as in the other known infrared-selected HyLIGs. In contrast, no high excitation lines are found in the non-hyperluminous ULIGs. We discuss the implications of our results for the number density of HyLIGs at z<1 and for the evolution of the infrared galaxy population out to this redshift, and show that substantial evolution is indicated. Our selection method is robust against the presence of gravitational lensing if the optical and infrared magnification factors are similar, and we suggest a way of using it to select candidate gravitationally lensed infrared galaxies.

astro-ph↗

arXiv1998

Dust and molecular gas in high redshift radio galaxies

This review discusses the current status of our knowledge of emission by dust and molecular gas in high redshift radio galaxies, and the uncertainties in the derivation of physical parameters from these data. The similarity of far-infrared luminous, gas-rich high redshift radio galaxies and local ultraluminous infrared galaxies (ULIGs) is discussed. Given that local ULIGs rapidly convert most of their gas reservoir into stars, far-infrared luminous high-z radio galaxies are likely undergoing immense bursts of star formation, possibly accounting for a large fraction of the final stellar populations in these systems. These results are discussed in the context of formation scenarios of massive galaxies.

astro-ph↗

arXiv1998

Observations and diagnostic use of highly redshifted fine structure lines

The diagnostic use and detectability of luminous fine structure lines from high redshift galaxies is reviewed in the light of results from COBE concerning the Milky Way and from ISO on low redshift galaxies. At the highest luminosities (L>10^{12}\Lsun) the [CII] 158 micron line is somewhat less luminous with respect to the bolometric luminosity than for lower luminosity objects. Thus, surveys for this line must emphasize depth. The [CII] line will be the principle spectroscopic probe of the deep universe for the MMA and FIRST. A deep search for [CII] 158 micron emission from the dusty z=4.693 quasar BR1202-0725 is presented. The resulting 3σupper limit implies that for this object L[CII]}/LFIR<0.0006%, a highly significant result indicating that distant luminous objects may represent a natural extension towards higher luminosities of the ultraluminous infrared galaxies at low redshift.

astro-ph↗

arXiv1997

Star formation at high redshift as traced by near-infrared Halpha surveys

Surveys of redshifted emission lines in the near-infrared will provide unique information on the cosmic star formation history. Near-infrared Halpha surveys will probe the cosmic star formation density and the evolution of the luminosity function of star forming galaxies out to z\sim2.5, including the important z=1.5-2.0 epoch, where according to current knowledge the cosmic star formation density peaks. Halpha and other hydrogen recombination lines (except Lyman alpha) and [O II] are all useful tracers of star formation provided the luminosity function is probed to sufficiently deep levels. However, shallow surveys or surveys of Lyman alpha or [O III] emission are not suitable for measuring or even constraining the cosmic star formation density. A first estimate of the star formation density at z\approx2.25 is derived, based on a new and sensitive large-area ESO near-infrared survey for Halpha emission at this redshift. Future observational directions, at near-infrared and longer wavelengths, for reading the cosmic star formation history are outlined.

astro-ph↗