arXiv subjects

Marc A. W. Verheijen

Publications and source records attributed to Marc A. W. Verheijen.

At least 37 records · Page 2Linked to original sources

arXiv2015

Gas-phase metallicity profiles of the Bluedisk galaxies: Is metallicity in a local star-formation regulated equilibrium?

As part of the Bluedisk survey we analyse the radial gas-phase metallicity profiles of 50 late-type galaxies We compare the metallicity profiles of a sample of HI-rich galaxies against a control sample of HI-'normal' galaxies. We find the metallicity gradient of a galaxy to be strongly correlated with its HI mass fraction (M(HI) / Mstar). We note that some galaxies exhibit a steeper metallicity profile in the outer disc than in the inner disc. These galaxies are found in both the HI-rich and control samples. This contradicts a previous indication that these outer drops are exclusive to HI-rich galaxies. These effects are not driven by bars, although we do find some indication that barred galaxies have flatter metallicity profiles. By applying a simple analytical model we are able to account for the variety of metallicity profiles that the two samples present. The success of this model implies that the metallicity in these isolated galaxies may be in a local equilibrium, regulated by star formation. This insight could provide an explanation of the observed local mass-metallicity relation.

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arXiv2015

BUDHIES II: A phase-space view of HI gas stripping and star-formation quenching in cluster galaxies

We investigate the effect of ram-pressure from the intracluster medium on the stripping of HI gas in galaxies in a massive, relaxed, X-ray bright, galaxy cluster at z=0.2 from the Blind Ultra Deep HI Environmental Survey (BUDHIES). We use cosmological simulations, and velocity vs. position phase-space diagrams to infer the orbital histories of the cluster galaxies. In particular, we embed a simple analytical description of ram-pressure stripping in the simulations to identify the regions in phase-space where galaxies are more likely to have been sufficiently stripped of their HI gas to fall below the detection limit of our survey. We find a striking agreement between the model predictions and the observed location of HI-detected and non-detected blue (late-type) galaxies in phase-space, strongly implying that ram-pressure plays a key role in the gas removal from galaxies, and that this can happen during their first infall into the cluster. However, we also find a significant number of gas-poor, red (early-type) galaxies in the infall region of the cluster that cannot easily be explained with our model of ram-pressure stripping alone. We discuss different possible additional mechanisms that could be at play, including the pre-processing of galaxies in their previous environment. Our results are strengthened by the distribution of galaxy colours (optical and UV) in phase-space, that suggests that after a (gas-rich) field galaxy falls into the cluster, it will lose its gas via ram-pressure stripping, and as it settles into the cluster, its star formation will decay until it is completely quenched. Finally, this work demonstrates the utility of phase-space diagrams to analyze the physical processes driving the evolution of cluster galaxies, in particular HI gas stripping.

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arXiv2014

The Link Between Light and Mass in Late-type Spiral Galaxy Disks

We present the correlation between the extrapolated central disk surface brightness (mu) and extrapolated central surface mass density (Sigma) for galaxies in the DiskMass sample. This mu-Sigma-relation has a small scatter of 30% at the high-surface-brightness (HSB) end. At the low surface brightness (LSB) end, galaxies fall above the mu-Sigma-relation, which we attribute to their higher dark matter content. After correcting for the dark matter, as well as for the contribution of gas and the effects of radial gradients in the disk, the LSB end falls back on the linear mu-Sigma-relation. The resulting scatter about the corrected mu-Sigma-relation is 25% at the HSB end, and about 50% at the LSB end. The intrinsic scatter in the mu-Sigma-relation is estimated to be 10% to 20%. Thus, if the surface brightness is known, the stellar surface mass density is known to within 10-20% (random error). Assuming disks have an exponential vertical distribution of mass, the average (M_L)_K is 0.24 Msun/Lsun, with an intrinsic scatter around the mean of at most 0.05 Msun/Lsun. This value for (M/L)_K is 20% smaller than we found in Martinsson et al., mainly due to the correction for dark matter applied here. This small scatter means that among the galaxies in our sample variations in scale height, vertical density profile shape, and/or the ratio of vertical over radial velocity dispersion must be small.

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arXiv2014

The DiskMass Survey. VIII. On the Relationship Between Disk Stability and Star Formation

We study the relationship between the stability level of late-type galaxy disks and their star-formation activity using integral-field gaseous and stellar kinematic data. Specifically, we compare the two-component (gas+stars) stability parameter from Romeo & Wiegert (Q_RW), incorporating stellar kinematic data for the first time, and the star-formation rate estimated from 21cm continuum emission. We determine the stability level of each disk probabilistically using a Bayesian analysis of our data and a simple dynamical model. Our method incorporates the shape of the stellar velocity ellipsoid (SVE) and yields robust SVE measurements for over 90% of our sample. Averaging over this subsample, we find a meridional shape of sigma_z/sigma_R = 0.51^{+0.36}_{-0.25} for the SVE and, at 1.5 disk scale lengths, a stability parameter of Q_RW = 2.0 +/- 0.9. We also find that the disk-averaged star-formation-rate surface density (Sigma-dot_e,*) is correlated with the disk-averaged gas and stellar mass surface densities (Sigma_e,g and Sigma_e,*) and anti-correlated with Q_RW. We show that an anti-correlation between Sigma-dot_e,* and Q_RW can be predicted using empirical scaling relations, such that this outcome is consistent with well-established statistical properties of star-forming galaxies. Interestingly, Sigma-dot_e,* is not correlated with the gas-only or star-only Toomre parameters, demonstrating the merit of calculating a multi-component stability parameter when comparing to star-formation activity. Finally, our results are consistent with the Ostriker et al. model of self-regulated star-formation, which predicts Sigma-dot_e,*/Sigma_e,g/sqrt(Sigma_e,*). Based on this and other theoretical expectations, we discuss the possibility of a physical link between disk stability level and star-formation rate in light of our empirical results.

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arXiv2013

The Stability of Galaxy Disks

We calculate the stellar surface mass density (Sigma_*) and two-component (gas+stars) disk stability (Q_RW) for 25 late-type galaxies from the DiskMass Survey. These calculations are based on fits of a dynamical model to our ionized-gas and stellar kinematic data performed using a Markov Chain Monte Carlo sampling of the Bayesian posterior. Marginalizing over all galaxies, we find a median value of Q_RW=2.0+/-0.9 at 1.5 scale lengths. We also find that Q_RW is anti-correlated with the star-formation rate surface density (Sigma_SFR), which can be predicted using a closed set of empirical scaling relations. Finally, we find that the star-formation efficiency (Sigma_SFR/Sigma_g) is correlated with Sigma_* and weakly anti-correlated with Q_RW. The former is consistent with an equilibrium prediction of Sigma_SFR/Sigma_g propto Sigma_*^{1/2}. Despite its order-of-magnitude range, we find no correlation of Sigma_SFR/Sigma_g/Sigma_*^{1/2} with any other physical quantity derived by our study.

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arXiv2013

The DiskMass Survey. VII. The distribution of luminous and dark matter in spiral galaxies

We present dynamically-determined rotation-curve mass decompositions of 30 spiral galaxies, which were carried out to test the maximum-disk hypothesis and to quantify properties of their dark-matter (DM) halos. We used measured vertical velocity dispersions of the disk stars to calculate dynamical mass surface densities. Together with our atomic and molecular gas mass surface densities, we derived the stellar mass surface densities, and thus have absolute measurements of all dominant baryonic components. Using K-band surface brightness profiles, we calculated the K-band mass-to-light ratio of the stellar disks (M/L). Our result is consistent with all galaxies in the sample having equal M/L, with a sample average and scatter of =0.31+/-0.07. Rotation-curves of the baryonic components were calculated from their mass surface densities, and used with circular-speed measurements to derive the structural parameters of the DM halos, modeled as either a pseudo-isothermal sphere (pISO) or an NFW halo. All galaxies in our sample are submaximal, such that at 2.2 disk scale lengths (hR) the ratios between the baryonic and total rotation-curves (Fb^{2.2hR}) are less than 0.75. We find this ratio to be nearly constant between 1-6 hR within individual galaxies. We find a sample average and scatter of =0.57+/-0.07, with trends of larger Fb^{2.2hR} for more luminous and higher-surface-brightness galaxies. To enforce these being maximal, we need to scale M/L by a factor 3.6 on average. The DM rotation curves are marginally better fit by a pISO than by an NFW halo. For the nominal-M/L (submaximal) case, the derived NFW-halo parameters have values consistent with LCDM N-body simulations, suggesting that the baryonic matter has only had a minor effect on the DM distribution. In contrast, maximum-M/L decompositions yield halo concentrations that are too low compared to the LCDM simulations.

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arXiv2013

The DiskMass Survey. VI. Gas and stellar kinematics in spiral galaxies from PPak integral-field spectroscopy

We present ionized-gas (OIII) and stellar kinematics (velocities and velocity dispersions) for 30 nearly face-on spiral galaxies out to as much as three disk scale lengths (h_R). These data have been derived from PPak IFU spectroscopy (4980-5370A), observed at a mean resolution of R=7700 (sigma_inst=17km/s). These data are a fundamental product of our survey and will be used in companion papers to, e.g., derive the detailed (baryonic+dark) mass budget of each galaxy in our sample. Our presentation provides a comprehensive description of the observing strategy, data reduction, and analysis. Along with a clear presentation of the data, we demonstrate: (1) The OIII and stellar rotation curves exhibit a clear signature of asymmetric drift with a rotation difference that is 11% of the maximum rotation speed of the galaxy disk, comparable to measurements in the solar neighborhood in the Milky Way. (2) The e-folding length of the stellar velocity dispersion is two times h_R on average, as expected for a disk with a constant scale height and mass-to-light ratio, with a scatter that is notably smaller for massive, high-surface-brightness disks in the most luminous galaxies. (3) At radii larger than 1.5 h_R, the stellar velocity dispersion tends to decline slower than the best-fitting exponential function, which may be due to an increase in the disk mass-to-light ratio, disk flaring, or disk heating by the dark-matter halo. (4) A strong correlation exists between the central vertical stellar velocity dispersion of the disks and their circular rotational speed at 2.2 h_R, with a zero point indicating that galaxy disks are submaximal. Moreover, weak but consistent correlations exist such that disks with a fainter central surface brightness in bluer and less luminous galaxies of later morphological types are kinematically colder with respect to their rotational velocities.

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arXiv2013

BUDHIES I: characterizing the environments in and around two clusters at z~0.2

We present the optical spectroscopy for the Blind Ultra Deep HI Environmental Survey (BUDHIES). With the Westerbork Synthesis Radio Telescope, BUDHIES has detected HI in over 150 galaxies in and around two Abell clusters at z~0.2. With the aim of characterizing the environments of the HI-detected galaxies, we obtained multi-fiber spectroscopy with the William Herschel Telescope. In this paper, we describe the spectroscopic observations, report redshifts and EW[OII] measurements for ~600 galaxies, and perform an environmental analysis. In particular, we present cluster velocity dispersion measurements for 5 clusters and groups in the BUDHIES volume, as well as a detailed substructure analysis.

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arXiv2011

Galaxy Disks are Submaximal

We measure the contribution of galaxy disks to the overall gravitational potential of 30 nearly face-on intermediate-to-late-type spirals from the DiskMass Survey. The central vertical velocity dispersion of the disk stars, sigma(z,R=0), is related to the maximum rotation speed (Vmax) as sigma(z,R=0) ~ 0.26 Vmax, consistent with previous measurements for edge-on disk galaxies and a mean stellar velocity ellipsoid axial ratio sigma(z) / sigma(R) = 0.6. For reasonable values of disk oblateness, this relation implies these galaxy disks are submaximal. We find disks in our sample contribute only 15% to 30% of the dynamical mass within 2.2 disk scale-lengths (hR), with percentages increasing systematically with luminosity, rotation speed and redder color. These trends indicate the mass ratio of disk-to-total matter remains at or below 50% at 2.2 hR even for the most extreme, fast-rotating disks (Vmax > 300 km/s), of the reddest rest-frame, face-on color (B-K ~ 4 mag), and highest luminosity (M(K)<-26.5 mag). Therefore, spiral disks in general should be submaximal. Our results imply that the stellar mass-to-light ratio and hence the accounting of baryons in stars should be lowered by at least a factor of 3.

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arXiv2011

The DiskMass Survey. IV. The Dark-Matter-Dominated Galaxy UGC 463

We present a detailed and unique mass budget for the high-surface-brightness galaxy UGC 463, showing it is dominated by dark matter (DM) at radii beyond one scale length (h_R) and has a baryonic-to-DM mass ratio of approximately 1:3 within 4.2 h_R. Assuming a constant scale height (h_z, calculated via an empirical oblateness relation), we calculate dynamical disk mass surface densities from stellar kinematics, which provide vertical velocity dispersions after correcting for the shape of the stellar velocity ellipsoid (measured to have sigma_theta/sigma_R=1.04 +/- 0.22 and sigma_z/sigma_R=0.48 +/- 0.09). We isolate the stellar mass surface density by accounting for all gas mass components and find an average K-band mass-to-light ratio of 0.22 +/- 0.09 (ran) ^{+0.16}_{-0.15} (sys) M_{sun}/L_{sun}^{K}; Zibetti et al. and Bell et al. predict, respectively, 0.56 and 3.6 times our dynamical value based on stellar-population-synthesis modeling. The baryonic matter is submaximal by a factor of ~3 in mass and the baryonic-to-total circular-speed ratio is 0.61^{+0.07}_{-0.09} (ran) ^{+0.12}_{-0.18} (sys) at 2.2 h_R; however, the disk is globally stable with a multi-component stability that decreases asymptotically with radius to Q~2. We directly calculate the circular speed of the DM halo by subtracting the baryonic contribution to the total circular speed; the result is equally well described by either a Navarro-Frenk-White halo or a pseudo-isothermal sphere. The volume density is dominated by DM at heights of |z|>1.6 h_z for radii of R > h_R. As is shown in follow-up papers, UGC 463 is just one example among nearly all galaxies we have observed that contradict the hypothesis that high-surface-brightness spiral galaxies have maximal disks.

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arXiv2010

Design drivers for a wide-field multi-object spectrograph for the William Herschel Telescope

Wide-field multi-object spectroscopy is a high priority for European astronomy over the next decade. Most 8-10m telescopes have a small field of view, making 4-m class telescopes a particularly attractive option for wide-field instruments. We present a science case and design drivers for a wide-field multi-object spectrograph (MOS) with integral field units for the 4.2-m William Herschel Telescope (WHT) on La Palma. The instrument intends to take advantage of a future prime-focus corrector and atmospheric-dispersion corrector that will deliver a field of view 2 deg in diameter, with good throughput from 370 to 1,000 nm. The science programs cluster into three groups needing three different resolving powers R: (1) high-precision radial-velocities for Gaia-related Milky Way dynamics, cosmological redshift surveys, and galaxy evolution studies (R = 5,000), (2) galaxy disk velocity dispersions (R = 10,000) and (3) high-precision stellar element abundances for Milky Way archaeology (R = 20,000). The multiplex requirements of the different science cases range from a few hundred to a few thousand, and a range of fibre-positioner technologies are considered. Several options for the spectrograph are discussed, building in part on published design studies for E-ELT spectrographs. Indeed, a WHT MOS will not only efficiently deliver data for exploitation of important imaging surveys planned for the coming decade, but will also serve as a test-bed to optimize the design of MOS instruments for the future E-ELT.

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arXiv2010

The DiskMass Survey. II. Error Budget

We present a performance analysis of the DiskMass Survey. The survey uses collisionless tracers in the form of disk stars to measure the surface-density of spiral disks, to provide an absolute calibration of the stellar mass-to-light ratio, and to yield robust estimates of the dark-matter halo density profile in the inner regions of galaxies. We find a disk inclination range of 25-35 degrees is optimal for our measurements, consistent with our survey design to select nearly face-on galaxies. Uncertainties in disk scale-heights are significant, but can be estimated from radial scale-lengths to 25% now, and more precisely in the future. We detail the spectroscopic analysis used to derive line-of-sight velocity dispersions, precise at low surface-brightness, and accurate in the presence of composite stellar populations. Our methods take full advantage of large-grasp integral-field spectroscopy and an extensive library of observed stars. We show that the baryon-to-total mass fraction (F_b) is not a well-defined observational quantity because it is coupled to the halo mass model. This remains true even when the disk mass is known and spatially-extended rotation curves are available. In contrast, the fraction of the rotation speed supplied by the disk at 2.2 scale lengths (disk maximality) is a robust observational indicator of the baryonic disk contribution to the potential. We construct the error-budget for the key quantities: dynamical disk mass surface-density, disk stellar mass-to-light ratio, and disk maximality (V_disk / V_circular). Random and systematic errors in these quantities for individual galaxies will be ~25%, while survey precision for sample quartiles are reduced to 10%, largely devoid of systematic errors outside of distance uncertainties.

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arXiv2010

The DiskMass Survey. I. Overview

We present a survey of the mass surface-density of spiral disks, motivated by outstanding uncertainties in rotation-curve decompositions. Our method exploits integral-field spectroscopy to measure stellar and gas kinematics in nearly face-on galaxies sampled at 515, 660, and 860 nm, using the custom-built SparsePak and PPak instruments. A two-tiered sample, selected from the UGC, includes 146 nearly face-on galaxies, with B<14.7 and disk scale-lengths between 10 and 20 arcsec, for which we have obtained H-alpha velocity-fields; and a representative 46-galaxy subset for which we have obtained stellar velocities and velocity dispersions. Based on re-calibration of extant photometric and spectroscopic data, we show these galaxies span factors of 100 in L(K) (0.03 < L/L(K)* < 3), 8 in L(B)/L(K), 10 in R-band disk central surface-brightness, with distances between 15 and 200 Mpc. The survey is augmented by 4-70 micron Spitzer IRAC and MIPS photometry, ground-based UBVRIJHK photometry, and HI aperture-synthesis imaging. We outline the spectroscopic analysis protocol for deriving precise and accurate line-of-sight stellar velocity dispersions. Our key measurement is the dynamical disk-mass surface-density. Star-formation rates and kinematic and photometric regularity of galaxy disks are also central products of the study. The survey is designed to yield random and systematic errors small enough (i) to confirm or disprove the maximum-disk hypothesis for intermediate-type disk galaxies, (ii) to provide an absolute calibration of the stellar mass-to-light ratio well below uncertainties in present-day stellar-population synthesis models, and (iii) to make significant progress in defining the shape of dark halos in the inner regions of disk galaxies.

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arXiv2008

Deconstructing Disk Velocity Distribution Functions in the Disk-Mass Survey

We analyze integral-field ionized gas and stellar line-of-sight kinematics in the context of determining the stellar velocity ellipsoid for spiral galaxies observed by the Disk-Mass Survey. Our new methodology enables us to measure, for the first time, a radial gradient in the ellipsoid ratio sigma_z / sigma_R. Random errors in this decomposition are 15% at two disk scale-lengths.

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arXiv2007

WSRT Ultra-Deep Neutral Hydrogen Imaging of Galaxy Clusters at z=0.2, a Pilot Survey of Abell 963 and Abell 2192

A pilot study with the powerful new backend of the Westerbork Synthesis Radio Telescope (WSRT) of two galaxy clusters at z=0.2 has revealed neutral hydrogen emission from 42 galaxies. The WSRT probes a total combined volume of 3.4x10^4 Mpc^3 at resolutions of 54x86 kpc^2 and 19.7 km/s, surveying both clusters and the large scale structure in which they are embedded. In Abell 963, a dynamically relaxed, lensing Butcher-Oemler cluster with a high blue fraction, most of the gas-rich galaxies are located between 1 and 3 Mpc in projection, northeast from the cluster core. Their velocities are slightly redshifted with respect to the cluster, and this is likely a background group. None of the blue galaxies in the core of Abell 963 are detected in HI, although they have similar colors and luminosities as the HI detected galaxies in the cluster outskirts and field. Abell 2192 is less massive and more diffuse. Here, the gas-rich galaxies are more uniformly distributed. The detected HI masses range from 5x10^9 to 4x10^10 Msun. Some galaxies are spatially resolved, providing rudimentary rotation curves useful for detailed kinematic studies of galaxies in various environments. This is a pilot for ultra-deep integrations down to HI masses of 8x10^8 Msun, providing a complete survey of the gas content of galaxies at z=0.2, probing environments ranging from cluster cores to voids.

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arXiv2005

PMAS: The Potsdam Multi Aperture Spectrophotometer. II. The Wide Integral Field Unit PPak

PPak is a new fiber-based Integral Field Unit (IFU), developed at the Astrophysical Institute Potsdam, implemented as a module into the existing PMAS spectrograph. The purpose of PPak is to provide both an extended field-of-view with a large light collecting power for each spatial element, as well as an adequate spectral resolution. The PPak system consists of a fiber bundle with 331 object, 36 sky and 15 calibration fibers. The object and sky fibers collect the light from the focal plane behind a focal reducer lens. The object fibers of PPak, each 2.7 arcseconds in diameter, provide a contiguous hexagonal field-of-view of 74 times 64 arcseconds on the sky, with a filling factor of 60%. The operational wavelength range is from 400 to 900nm. The PPak-IFU, together with the PMAS spectrograph, are intended for the study of extended, low surface brightness objects, offering an optimization of total light-collecting power and spectral resolution. This paper describes the instrument design, the assembly, integration and tests, the commissioning and operational procedures, and presents the measured performance at the telescope.

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arXiv2005

The Disk Mass Project: breaking the disk-halo degeneracy

Little is known about the content and distribution of dark matter in spiral galaxies. To break the degeneracy in galaxy rotation curve decompositions, which allows a wide range of dark matter halo density profiles, an independent measure of the mass surface density of stellar disks is needed. Here, we present our ongoing Disk Mass project, using two custom-built Integral Field Units, to measure the vertical velocity dispersion of stars in ~40 spiral galaxies. This will provide a kinematic measurement of the stellar disk mass required to break the degeneracy, enabling us to determine the dark matter properties in spiral galaxies with unprecedented accuracy. Here we present preliminary results for three galaxies with different central disk surface brightness levels.

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arXiv2005

Asymmetric Drift and the Stellar Velocity Ellipsoid

We present the decomposition of the stellar velocity ellipsoid using stellar velocity dispersions within a 40 deg wedge about the major-axis (sigma_maj), the epicycle approximation, and the asymmetric drift equation. Thus, we employ no fitted forms for sigma_maj and escape interpolation errors resulting from comparisons of the major and minor axes. We apply the theoretical construction of the method to integral field data taken for NGC 3949 and NGC 3982. We derive the vertical-to-radial velocity dispersion ratio (sigma_z / sigma_R) and find (1) our decomposition method is accurate and reasonable, (2) NGC 3982 appears to be rather typical of an Sb type galaxy with sigma_z / sigma_R = 0.73 (+0.13/-0.11) despite its high surface brightness and small size, and (3) NGC 3949 has a hot disk with sigma_z / sigma_R = 1.18 (+0.36/-0.28).

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