arXiv subjects

Oliver Czoske

Publications and source records attributed to Oliver Czoske.

At least 19 recordsLinked to original sources

arXiv2022

Observing Circumplanetary Disks with METIS

Context: A full understanding of the planet and moon formation process requires observations that probe the circumplanetary environment of accreting giant planets. The mid-infrared ELT imager and spectrograph (METIS) will provide a unique capability to detect warm-gas emission lines from circumplanetary disks. Aims: We aim to demonstrate the capability of the METIS instrument on the Extremely Large Telescope (ELT) to detect circumplanetary disks (CPDs) with fundamental v=1-0 transitions of $^{12}$CO from 4.5-5 $μ$m. Methods: We consider the case of the well-studied HD 100546 pre-transitional disk to inform our disk modeling approach. We use the radiation-thermochemical disk modeling code ProDiMo to produce synthetic spectral channel maps. The observational simulator SimMETIS is employed to produce realistic data products with the integral field spectroscopic (IFU) mode. Results: The detectability of the CPD depends strongly on the level of external irradiation and the physical extent of the disk, favoring massive (~10 M$_{\rm J}$) planets and spatially extended disks with radii approaching the planetary Hill radius. The majority of $^{12}$CO line emission originates from the outer disk surface, and thus the CO line profiles are centrally peaked. The planetary luminosity does not contribute significantly to exciting disk gas line emission. If CPDs are dust-depleted, the $^{12}$CO line emission is enhanced as external radiation can penetrate deeper into the line emitting region. Conclusions: UV-bright star systems with pre-transitional disks are ideal candidates to search for CO-emitting CPDs with ELT/METIS. METIS will be able to detect a variety of circumplanetary disks via their fundamental $^{12}$CO ro-vibrational line emission in only 60 s of total detector integration time.

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arXiv2021

ScopeSim: A flexible general purpose astronomical instrument data simulation framework in Python

ScopeSim is a flexible multipurpose instrument data simulation framework built in Python. It enables both raw and reduced observation data to be simulated for a wide range of telescopes and instruments quickly and efficiently on a personal computer. The software is currently being used to generate simulated raw input data for developing the data reduction pipelines for the MICADO and METIS instruments at the ELT. The ScopeSim environment consists of three main packages which are responsible for providing on-sky target templates (ScopeSim_templates), the data to build the optical models of various telescopes and instruments (instrument reference database), and the simulation engine (ScopeSim). This strict division of responsibilities allows ScopeSim to be used to simulate observation data for many different instrument and telescope configurations for both imaging and spectroscopic instruments. ScopeSim has been built to avoid redundant calculations wherever possible. As such it is able to deliver simulated observations on time scales of seconds to minutes. All the code and data is open source and hosted on Github. The community is also most welcome, and indeed encouraged to contribute to code ideas, target templates, and instrument packages.

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arXiv2018

The MICADO first light imager for the ELT: overview, operation, simulation

MICADO will enable the ELT to perform diffraction limited near-infrared observations at first light. The instrument's capabilities focus on imaging (including astrometric and high contrast) as well as single object spectroscopy. This contribution looks at how requirements from the observing modes have driven the instrument design and functionality. Using examples from specific science cases, and making use of the data simulation tool, an outline is presented of what we can expect the instrument to achieve.

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arXiv2018

The Sloan Lens ACS Survey. XIII. Discovery of 40 New Galaxy-Scale Strong Lenses

We present the full sample of 118 galaxy-scale strong-lens candidates in the Sloan Lens ACS (SLACS) Survey for the Masses (S4TM) Survey, which are spectroscopically selected from the final data release of the Sloan Digital Sky Survey. Follow-up Hubble Space Telescope (HST) imaging observations confirm that 40 candidates are definite strong lenses with multiple lensed images. The foreground lens galaxies are found to be early-type galaxies (ETGs) at redshifts 0.06 to 0.44, and background sources are emission-line galaxies at redshifts 0.22 to 1.29. As an extension of the SLACS Survey, the S4TM Survey is the first attempt to preferentially search for strong-lens systems with relatively lower lens masses than those in the pre-existing strong-lens samples. By fitting HST data with a singular isothermal ellipsoid model, we find total projected mass within the Einstein radius of the S4TM strong-lens sample ranges from $3 \times10^{10} M_{\odot}$ to $2 \times10^{11} M_{\odot}$. In [Shu15], we have derived the total stellar mass of the S4TM lenses to be $5 \times10^{10} M_{\odot}$ to $1 \times10^{12} M_{\odot}$. Both total enclosed mass and stellar mass of the S4TM lenses are on average almost a factor of 2 smaller than those of the SLACS lenses, which also represent typical mass scales of the current strong-lens samples. The extended mass coverage provided by the S4TM sample can enable a direct test, with the aid of strong lensing, for transitions in scaling relations, kinematic properties, mass structure, and dark-matter content trends of ETGs at intermediate-mass scales as noted in previous studies.

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arXiv2016

SimCADO - an instrument data simulator package for MICADO at the E-ELT

MICADO will be the first-light wide-field imager for the European Extremely Large Telescope (E-ELT) and will provide difiraction limited imaging (7mas at 1.2mm) over a ~53 arcsecond field of view. In order to support various consortium activities we have developed a first version of SimCADO: an instrument simulator for MICADO. SimCADO uses the results of the detailed simulation efforts conducted for each of the separate consortium-internal work packages in order to generate a model of the optical path from source to detector readout. SimCADO is thus a tool to provide scientific context to both the science and instrument development teams who are ultimately responsible for the final design and future capabilities of the MICADO instrument. Here we present an overview of the inner workings of SimCADO and outline our plan for its further development.

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arXiv2015

The Sloan Lens ACS Survey. XII. Extending Strong Lensing to Lower Masses

We present observational results from a new Hubble Space Telescope (HST) Snapshot program to extend the methods of the Sloan Lens ACS (SLACS) Survey to lower lens-galaxy masses. We discover 40 new galaxy-scale strong lenses, which we supplement with 58 previously discovered SLACS lenses. In addition, we determine the posterior PDFs of the Einstein radius for 33 galaxies (18 new and 15 from legacy SLACS data) based on single lensed images. We find a less-than-unity slope of $0.64\pm0.06$ for the $\log_{10} σ_*$-$\log_{10} σ_{\rm SIE}$ relation, which corresponds to a 6-$σ$ evidence that the total mass-density profile of early-type galaxies varies systematically in the sense of being shallower at higher lens-galaxy velocity dispersions. The trend is only significant when single-image systems are considered, highlighting the importance of including both "lenses" and "non-lenses" for an unbiased treatment of the lens population when extending to lower mass ranges. By scaling simple stellar population models to the HST I-band data, we identify a strong trend of increasing dark-matter fraction at higher velocity dispersions, which can be alternatively interpreted as a trend in the stellar initial mass function (IMF) normalization. Consistent with previous findings and the suggestion of a non-universal IMF, we find that a Salpeter IMF is ruled out for galaxies with velocity dispersion less than $180$ km/s. Considered together, our mass-profile and dark-matter-fraction trends with increasing galaxy mass could both be explained by an increasing relative contribution on kiloparsec scales from a dark-matter halo with a spatial profile more extended than that of the stellar component.

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arXiv2014

CLASH-VLT: Is there a dependence in metallicity evolution on galaxy structures?

We investigate the environmental dependence of the mass-metallicty (MZ) relation and it's connection to galaxy stellar structures and morphologies. In our studies, we analyze galaxies in massive clusters at z~0.4 from the CLASH (HST) and CLASH-VLT surveys and measure their gas metallicities, star-formation rates, stellar structures and morphologies. We establish the MZ relation for 90 cluster and 40 field galaxies finding a shift of ~-0.3 dex in comparison to the local trends seen in SDSS for the majority of galaxies with logM<10.5. We do not find significant differences of the distribution of 4 distinct morphological types that we introduce by our classification scheme (smooth, disc-like, peculiar, compact). Some variations between cluster and field galaxies in the MZ relation are visible at the high mass end. However, obvious trends for cluster specific interactions (enhancements or quenching of SFRs) are missing. In particular, galaxies with peculiar stellar structures that hold signs for galaxy interactions, are distributed in a similar way as disc-like galaxies - in SFRs, masses and O/H abundances. We further show that our sample falls around an extrapolation of the star-forming main sequence (the SFR-M* relation) at this redshift, indicating that emission-line selected samples do not have preferentially high star-formation rates (SFRs). However, we find that half of the high mass cluster members (M*>10^10Msun) lie below the main sequence which corresponds to the higher mass objects that reach solar abundances in the MZ diagram.

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arXiv2014

Weighing the Giants II: Improved Calibration of Photometry from Stellar Colors and Accurate Photometric Redshifts

We present improved methods for using stars found in astronomical exposures to calibrate both star and galaxy colors as well as to adjust the instrument flat field. By developing a spectroscopic model for the SDSS stellar locus in color-color space, synthesizing an expected stellar locus, and simultaneously solving for all unknown zeropoints when fitting to the instrumental locus, we increase the calibration accuracy of stellar locus matching. We also use a new combined technique to estimate improved flat-field models for the Subaru SuprimeCam camera, forming `star flats' based on the magnitudes of stars observed in multiple positions or through comparison with available SDSS magnitudes. These techniques yield galaxy magnitudes with reliable color calibration (< 0.01 - 0.02 mag accuracy) that enable us to estimate photometric redshift probability distributions without spectroscopic training samples. We test the accuracy of our photometric redshifts using spectroscopic redshifts z_s for ~5000 galaxies in 27 cluster fields with at least five bands of photometry, as well as galaxies in the COSMOS field, finding sigma((z_p - z_s)/(1 + z_s)) ~ 0.03 for the most probable redshift z_p. We show that the full posterior probability distributions for the redshifts of galaxies with five-band photometry exhibit good agreement with redshifts estimated from thirty-band photometry in the COSMOS field. The growth of shear with increasing distance behind each galaxy cluster shows the expected redshift-distance relation for a flat Lambda-CDM cosmology. Photometric redshifts and calibrated colors are used in subsequent papers to measure the masses of 51 galaxy clusters from their weak gravitational shear. We make our Python code for stellar locus matching available at http://big-macs-calibrate.googlecode.com; the code requires only a catalog and filter functions.

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arXiv2014

CLASH-VLT: Constraints on the Dark Matter Equation of State from Accurate Measurements of Galaxy Cluster Mass Profiles

A pressureless scenario for the Dark Matter (DM) fluid is a widely adopted hypothesis, despite the absence of a direct observational evidence. According to general relativity, the total mass-energy content of a system shapes the gravitational potential well, but different test particles perceive this potential in different ways depending on their properties. Cluster galaxy velocities, being $\ll$c, depend solely on the gravitational potential, whereas photon trajectories reflect the contributions from the gravitational potential plus a relativistic-pressure term that depends on the cluster mass. We exploit this phenomenon to constrain the Equation of State (EoS) parameter of the fluid, primarily DM, contained in galaxy clusters. We use the complementary information provided by the kinematic and lensing mass profiles of the galaxy cluster MACS 1206.2-0847 at $z=0.44$, as obtained in an extensive imaging and spectroscopic campaign within the CLASH survey. The unprecedented high quality of our data-set and the properties of this cluster are well suited to determine the EoS parameter of the cluster fluid. Since baryons contribute at most $15\%$ to the total mass in clusters and their pressure is negligible, the EoS parameter we derive describes the behavior of the DM fluid. We obtain the most stringent constraint on the DM EoS parameter to date, $w=(p_r+2\,p_t)/(3\,c^2ρ)=0.00\pm0.15\mathrm{(stat)}\pm0.08\mathrm{(syst)}$, averaged over the radial range $0.5\,\mathrm{Mpc}\leq$$r$$\leq$$r_{200}$, where $p_r$ and $p_t$ are the radial and tangential pressure, and $ρ$ is the density. We plan to further improve our constraint by applying the same procedure to all clusters from the ongoing CLASH-VLT program.

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arXiv2013

A low-mass cut-off near the hydrogen burning limit for Salpeter-like initial mass functions in early-type galaxies

We conduct a detailed investigation of the properties of the stellar initial mass function (IMF) in two massive early-type lens galaxies with velocity dispersions of sigma ~245 km/s and sigma ~325 km/s, for which both HST imaging and X-Shooter spectra are available. We compare the inferences obtained from two fully independent methods: (i) a combined gravitational lensing and stellar dynamics (L&D) analysis of the data sets employing self-consistent axisymmetric models, and (ii) a spectroscopic simple stellar population (SSP) analysis of optical line-strength indices, assuming single power-law IMFs. The results from the two approaches are found to be in agreement within the 1-sigma uncertainties. Both galaxies are consistent with having a Salpeter IMF (power-law slope of x = 2.35), which is strongly favoured over a Chabrier IMF (x = 1.8), with probabilities inferred from the joint analysis of 89% and 99%, respectively. Bottom-heavy IMFs significantly steeper than Salpeter (x >= 3.0) are ruled out with decisive evidence (Bayes factor B > 1000) for both galaxies, as they exceed the total mass derived from the L&D constraints. Our analysis allows, for the first time, the inference of the low-mass cut-off of the IMF (M_low). Combining the joint L&D and SSP analyses of both galaxies, we infer an IMF slope of x = 2.22 +/- 0.14, consistent with Salpeter IMF, and a low-mass limit M_low = 0.13 +/- 0.03 M_sun, just above the hydrogen burning limit.

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arXiv2011

Two-dimensional kinematics of SLACS lenses - IV. The complete VLT-VIMOS data set

This paper presents the full VLT/VIMOS-IFU data set and related data products from an ESO Large Programme with the observational goal of obtaining two-dimensional kinematic data of early-type lens galaxies, out to one effective radius. The sample consists of 17 early-type galaxies (ETG) selected from the SLACS gravitational-lens survey. The galaxies cover the redshift range from 0.08 to 0.35 and have stellar velocity dispersions between 200 and 350 km/s. This programme is complemented by a similar observational programme on Keck, using long-slit spectroscopy. In combination with multi-band imaging data, the kinematic data provide stringent constraints on the inner mass profiles of ETGs beyond the local universe. Our Large Programme thus extends studies of nearby early-type galaxies (e.g. SAURON/ATLAS3D) by an order of magnitude in distance and toward higher masses. We provide an overview of our observational strategy, the data products (luminosity-weighted spectra and Hubble Space Telescope images) and derived products (i.e. two-dimensional fields of velocity dispersions and streaming motions) that have been used in a number of published and forthcoming lensing, kinematic and stellar-population studies.These studies also pave the way for future studies of early-type galaxies at z=1 with the upcoming extremely large telescopes.

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arXiv2011

Two-dimensional kinematics of SLACS lenses: III. Mass structure and dynamics of early-type lens galaxies beyond z ~ 0.1

We combine in a self-consistent way the constraints from both gravitational lensing and stellar kinematics to perform a detailed investigation of the internal mass distribution, amount of dark matter, and dynamical structure of the 16 early-type lens galaxies from the SLACS Survey, at z = 0.08 - 0.33, for which both HST/ACS and NICMOS high-resolution imaging and VLT VIMOS IFU spectroscopy are available. Based on this data set, we analyze the inner regions of the galaxies, i.e. typically within one (3D) effective radius r_e, under the assumption of axial symmetry and by constructing dynamical models supported by two-integral stellar DFs. For all systems, the total mass density distribution is found to be well approximated by a simple power-law: this profile is on average slightly super-isothermal, with a logarithmic slope = 2.074^{+0.043}_{-0.041} (68% CL) and an intrinsic scatter 0.144^{+0.055}_{-0.014}, and is fairly round, with an average axial ratio = 0.77+/-0.04. The lower limit for the dark matter fraction (fDM) inside r_e ranges, in individual systems, from nearly zero to almost a half, with a median value of 12%. By including stellar masses derived from SPS models with a Salpeter IMF, we obtain an average fDM = 31%. The fDM rises to 61% if, instead, a Chabrier IMF is assumed. For both IMFs, the dark matter fraction increases with the total mass of the galaxy (3-sigma correlation). Based on the intrinsic angular momentum parameter calculated from our models, we find that the galaxies can be divided into two dynamically distinct groups, which are shown to correspond to the usual classes of the slow and fast rotators. Overall, the SLACS systems are structurally and dynamically very similar to their nearby counterparts, indicating that the inner regions of early-type galaxies have undergone little, if any, evolution since redshift z ~ 0.35. (Abridged)

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arXiv2010

The non-evolving internal structure of early-type galaxies: the case study SDSS J0728+3835 at z = 0.206

We study the internal dynamical structure of the early-type lens galaxy SDSS J0728+3835 at z = 0.206. The analysis is based on two-dimensional kinematic maps extending out to 1.7 effective radii obtained from Keck spectroscopy, on lensing geometry and on stellar mass estimates obtained from multiband Hubble Space Telescope imaging. The data are modelled under the assumptions of axial symmetry supported by a two-integral distribution function (DF), by applying the combined gravitational lensing and stellar dynamics code CAULDRON, and yielding high-quality constraints for an early-type galaxy at cosmological redshifts. Modelling the total density profile as a power-law of the form rho_tot ~ 1/r^{gamma}, we find that it is nearly isothermal (logarithmic slope gamma = 2.08^{+0.04}_{-0.02}), and quite flattened (axial ratio q = 0.60^{+0.08}_{-0.03}). The galaxy is mildly anisotropic (delta = 0.08 +/- 0.02) and shows a fair amount of rotational support, in particular towards the outer regions. We determine a dark matter fraction lower limit of 28 per cent within the effective radius. The stellar contribution to the total mass distribution is close to maximal for a Chabrier initial mass function (IMF), whereas for a Salpeter IMF the stellar mass exceeds the total mass within the galaxy inner regions. We find that the combination of a NFW dark matter halo with the maximally rescaled luminous profile provides a remarkably good fit to the total mass distribution over a broad radial range. Our results confirm and expand the findings of the SLACS survey for early-type galaxies of comparable velocity dispersion (sigma_SDSS = 214 +/- 11 km/s). The internal structure of J0728 is consistent with that of local early-type galaxies of comparable velocity dispersion as measured by the SAURON project, suggesting lack of evolution in the past two billion years.

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arXiv2009

Two-dimensional kinematics of SLACS lenses: II. Combined lensing and dynamics analysis of early-type galaxies at z = 0.08 - 0.33

We present the first detailed analysis of the mass and dynamical structure of a sample of six early-type lens galaxies, selected from the Sloan Lens ACS Survey, in the redshift range 0.08 < z < 0.33. Both Hubble Space Telescope (HST)/ACS high-resolution imaging and VLT VIMOS integral field spectroscopy are available for these systems. The galaxies are modelled - under the assumptions of axial symmetry and two-integral stellar distribution function - by making use of the CAULDRON code, which self-consistently combines gravitational lensing and stellar dynamics, and is fully embedded within the framework of Bayesian statistics. The principal results of this study are: (i) all galaxies in the sample are well described by a simple axisymmetric power-law profile for the total density, with a logarithmic slope gamma very close to isothermal ( = 1.98 +/- 0.05 and an intrinsic spread close to 5 per cent) showing no evidence of evolution over the probed range of redshift; (ii) the axial ratio of the total density distribution is rounder than 0.65 and in all cases, except for a fast rotator, does not deviate significantly from the flattening of the intrinsic stellar distribution; (iii) the dark matter fraction within the effective radius has a lower limit of about 15 to 30 per cent; (iv) the sample galaxies are only mildly anisotropic, with delta <= 0.16; (v) the physical distinction among slow and fast rotators, quantified by the v/sigma ratio and the intrinsic angular momentum, is already present at z > 0.1. Altogether, early-type galaxies at z = 0.08 - 0.33 are found to be markedly smooth and almost isothermal systems, structurally and dynamically very similar to their nearby counterparts. (Abridged)

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arXiv2008

Integral-field spectroscopy of SLACS lenses

The combination of two-dimensional kinematics and gravitational lens modelling permits detailed reconstruction of the phase-space structure of early-type galaxies and sets constraints on the dark-matter distribution in their inner regions. We describe a project which combines integral-field spectroscopy from an ESO Large Programme using VIMOS on the VLT with deep HST ACS and NICMOS images to study a sample of 17 early-type lens galaxies at redshifts between 0.1 and 0.3, drawn from the Sloan Lens ACS survey (SLACS).

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arXiv2008

The survival of dark matter halos in the cluster Cl0024+16

Theories of structure formation in a cold dark matter dominated Universe predict that massive clusters of galaxies assemble from the hierarchical merging of lower mass subhalos. Exploiting strong and weak gravitational lensing signals inferred from panoramic HST imaging data, we present a high resolution reconstruction of the mass distribution in the massive, lensing cluster Cl0024+16. Applying galaxy-galaxy lensing techniques we track the fate of dark matter subhalos as a function of projected cluster-centric radius out to 5 Mpc, well beyond the virial radius. We report the first detection of the statistical lensing signal of dark matter subhalos associated with late-type galaxies in clusters. The mass of a typical dark matter subhalo that hosts an L* galaxy increases with projected cluster-centric radius in line with expectations from the tidal stripping hypothesis. Early-type galaxies appear to be hosted on average in more massive dark matter subhalos compared to late-type galaxies. We interpret our findings as evidence for the active assembly of mass via tidal stripping in galaxy clusters. The mass function of dark matter subhalos as a function of projected cluster-centric radius, is compared with an equivalent mass function derived from clusters in the Millenium Run simulation populated with galaxies using semi-analytic models. The shape of the lensing determined mass functions are in very good agreement with the subhalo mass functions derived from the Millenium Run simulation. However, simulated subhalos appear to be more efficiently stripped than lensing observations suggest. (Abridged)

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arXiv2008

Two-dimensional kinematics of SLACS lenses: I. Phase-space analysis of the early-type galaxy SDSS J2321-097 at z=0.1

We present the first results of a combined VLT VIMOS integral-field unit and Hubble Space Telescope (HST)/ACS study of the early-type lens galaxy SDSS J2321-097 at z=0.0819, extending kinematic studies to a look-back time of 1 Gyr. This system, discovered in the Sloan Lens ACS Survey (SLACS), has been observed as part of a VLT Large Programme with the goal of obtaining two-dimensional stellar kinematics of 17 early-type galaxies to z~0.35 and Keck spectroscopy of an additional dozen lens systems. Bayesian modelling of both the surface brightness distribution of the lensed source and the two-dimensional measurements of velocity and velocity dispersion has allowed us, under the only assumptions of axisymmetry and a two-integral stellar distribution function (DF) for the lens galaxy, to dissect this galaxy in three dimensions and break the classical mass--anisotropy, mass-sheet and inclination--oblateness degeneracies. Our main results are that the galaxy (i) has a total density profile well described by a single power-law rho propto r^{-gamma'} with gamma'=2.06^{+0.03}_{-0.06}; (ii) is a very slow rotator (specific stellar angular momentum parameter lambda_R = 0.075); (iii) shows only mild anisotropy (delta ~ 0.15); and (iv) has a dark matter contribution of ~30 per cent inside the effective radius. Our first results from this large combined imaging and spectroscopic effort with the VLT, Keck and HST show that the structure of massive early-type galaxies beyond the local Universe can now be studied in great detail using the combination of stellar kinematics and gravitational lensing. Extending these studies to look-back times where evolutionary effects become measurable holds great promise for the understanding of formation and evolution of early-type galaxies.

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arXiv2007

A statistical study of multiply-imaged systems in the lensing cluster Abell 68

We have carried out an extensive spectroscopic survey with the Keck and VLT telescopes, targeting lensed galaxies in the background of the massive cluster Abell 68. Spectroscopic measurements are obtained for 26 lensed images, including a distant galaxy at z=5.4 . Redshifts have been determined for 5 out of 7 multiply-image systems. Through a careful modeling of the mass distribution in the strongly-lensed regime, we derive a mass estimate of 5.3 x 10^14 Msun within 500 kpc. Our mass model is then used to constrain the redshift distribution of the remaining multiply-imaged and singly-imaged sources. This enables us to examine the physical properties for a subsample of 7 Lyman-alpha emitters at 1.7 < z < 5.5, whose unlensed luminosities of ~ 10^41 ergs/s are fainter than similar objects found in blank fields. Of particular interest is an extended Lyman-alpha emission region surrounding a highly magnified source at z=2.6, detected in VIMOS Integral Field Spectroscopy data. The physical scale of the most distant lensed source at z=5.4 is very small (<300 pc), similar to the lensed z ~ 5.6 emitter reported by Ellis et al. (2001) in Abell 2218. New photometric data available for Abell 2218 allow for a direct comparison between these two unique objects. Our survey illustrates the practicality of using lensing clusters to probe the faint end of the z ~ 2-5 Lyman-alpha luminosity function in a manner that is complementary to blank field narrow-band surveys.

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