Tucson, AZ, United States
Tucson, AZ, United States

Time filter

Source Type

Thalmann C.,ETH Zurich | Thalmann C.,University of Amsterdam | Mulders G.D.,University of Amsterdam | Mulders G.D.,University of Arizona | And 17 more authors.
Astronomy and Astrophysics | Year: 2014

We present four new epochs of Ks-band images of the young pre-transitional disk around LkCa 15 and perform extensive forward modeling to derive the physical parameters of the disk. We find indications of strongly anisotropic scattering (Henyey-Greenstein g = 0.67-0.11 +0.18) and a significantly tapered gap edge ("round wall") but see no evidence that the inner disk, whose existence is predicted by the spectral energy distribution, shadows the outer regions of the disk visible in our images. We marginally confirm the existence of an offset between the disk center and the star along the line of nodes; however, the magnitude of this offset (x = 27-20+19 mas) is notably lower than that found in our earlier H-band images. Intriguingly, we also find an offset of y=69 -25+49 mas perpendicular to the line of nodes at high significance. If confirmed by future observations, this would imply a highly elliptical - or otherwise asymmetric - disk gap with an effective eccentricity of e ≈ 0.3. Such asymmetry would most likely be the result of dynamical sculpting by one or more unseen planets in the system. Finally, we find that the bright arc of scattered light we see in direct imaging observations originates from the near side of the disk and appears brighter than the far side because of strong forward scattering. © ESO, 2014.

Krawczynski H.S.,Washington University in St. Louis | Stern D.,Jet Propulsion Laboratory | Harrison F.A.,California Institute of Technology | Kislat F.F.,Washington University in St. Louis | And 49 more authors.
Astroparticle Physics | Year: 2016

This paper describes the Polarization Spectroscopic Telescope Array (PolSTAR), a mission proposed to NASA's 2014 Small Explorer (SMEX) announcement of opportunity. PolSTAR measures the linear polarization of 3-50 keV (requirement; goal: 2.5-70 keV) X-rays probing the behavior of matter, radiation and the very fabric of spacetime under the extreme conditions close to the event horizons of black holes, as well as in and around magnetars and neutron stars. The PolSTAR design is based on the technology developed for the Nuclear Spectroscopic Telescope Array (NuSTAR) mission launched in June 2012. In particular, it uses the same X-ray optics, extendable telescope boom, optical bench, and CdZnTe detectors as NuSTAR. The mission has the sensitivity to measure ∼1% linear polarization fractions for X-ray sources with fluxes down to ∼5 mCrab. This paper describes the PolSTAR design as well as the science drivers and the potential science return. © 2015 Elsevier B.V.

Rasappu N.,Leiden University | Smit R.,Durham University | Labbe I.,Leiden University | Bouwens R.J.,Leiden University | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2016

Recent Spitzer/InfraRed Array Camera (IRAC) photometric observations have revealed that rest-frame optical emission lines contribute significantly to the broad-band fluxes of highredshift galaxies. Specifically, in the narrow redshift range z ~ 5.1-5.4 the [3.6]-[4.5] colour is expected to be very red, due to contamination of the 4.5 μm band by the dominant Ha line, while the 3.6 μmfilter is free of nebular emission lines.We take advantage of newreductions of deep Spitzer/IRAC imaging over the Great Observatories Origins Deep Survey-North+South fields (Labbé et al. 2015) to obtain a clean measurement of the mean Ha equivalent width (EW) from the [3.6]-[4.5] colour in the redshift range z = 5.1-5.4. The selected sources either have measured spectroscopic redshifts (13 sources) or lie very confidently in the redshift range z = 5.1-5.4 based on the photometric redshift likelihood intervals (11 sources). Our zphot = 5.1-5.4 sample and zspec = 5.10-5.40 spectroscopic sample have a mean [3.6]-[4.5] colour of 0.31 ± 0.05 and 0.35 ± 0.07 mag, implying a rest-frame EW (Hα+[N II]+[S II]) of 665 ± 53 and 707 ± 74 Å, respectively, for sources in these samples. These values are consistent albeit slightly higher than derived by Stark et al. at z ~ 4, suggesting an evolution to higher values of the Hα+[N II]+[S II] EWat z > 2. Using the 3.6 μm band, which is free of emission line contamination, we perform robust spectral energy distribution fitting and find a median specific star formation rate of sSFR = 17+2 -5 Gyr-1, 7+1 -2 × higher than at z ~ 2. We find no strong correlation (<2σ) between the Hα+[N II]+[S II] EW and the stellar mass of sources. Before the advent of JWST, improvements in these results will come through an expansion of current spectroscopic samples and deeper Spitzer/IRAC measurements. © 2016 The Authors.

Kovacs A.,California Institute of Technology | Kovacs A.,University of Minnesota | Barry P.S.,University of Cardiff | Bradford C.M.,Jet Propulsion Laboratory | And 17 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

SuperSpec is a pathfinder for future lithographic spectrometer cameras, which promise to energize extra-galactic astrophysics at (sub)millimeter wavelengths: delivering 200-500 kms-1 spectral velocity resolution over an octave bandwidth for every pixel in a telescope's field of view. We present circuit simulations that prove the concept, which enables complete millimeter-band spectrometer devices in just a few square-millimeter footprint. We evaluate both single-stage and two-stage channelizing filter designs, which separate channels into an array of broad-band detectors, such as bolometers or kinetic inductance detector (KID) devices. We discuss to what degree losses (by radiation or by absorption in the dielectric) and fabrication tolerances affect the resolution or performance of such devices, and what steps we can take to mitigate the degradation. Such design studies help us formulate critical requirements on the materials and fabrication process, and help understand what practical limits currently exist to the capabilities these devices can deliver today or over the next few years. © 2012 SPIE.

Mauskopf P.D.,University of Cardiff | Horner P.F.,University of Cardiff | Aguirre J.,University of Pennsylvania | Bock J.J.,Jet Propulsion Laboratory | And 6 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2012

We present an analysis of an 8-arcmin diameter map of the area around the galaxy cluster Abell 1835 from jiggle-map observations at a wavelength of 1.1mm using the Bolometric Camera (Bolocam) mounted on the Caltech Submillimeter Observatory (CSO). The data are well described by a model including a extended Sunyaev-Zel'dovich (SZ) emission from the cluster gas plus emission from the cluster central galaxy and two bright background submm galaxies magnified by the gravitational lensing of the cluster. We measure flux densities of the two bright point sources in the field: SMM J14011+0252 and SMM J14009+0252 to be 6.5 ± 2.0 ± 0.8 and 11.3 ± 1.9 ± 1.3mJy, respectively. Fitting the map to a sky model consisting of the point sources and the SZ emission from the cluster gas with a beta model density profile with parameters, θ c= 33.6arcsec and β= 0.69, we find the peak surface brightness of the SZ emission to be I c= 3.73 ± 0.45 ± 0.60 × 10 -21Wm -2sr -1Hz -1, where the first error is the statistical uncertainty in the fit and the second error represents the calibration uncertainty and additional systematics. Assuming zero cluster peculiar velocity and an X-ray temperature of T e= 9keV, this surface brightness corresponds to a central Comptonization of y 0= (4.41 ± 0.53 ± 0.70) × 10 -4. The cluster image represents one of the highest significance SZ detections of a cluster in the positive region of the thermal SZ spectrum to date. We compare the measured central intensity at 1.1mm to other SZ measurements of Abell 1835 at different wavelengths to obtain values for y 0= (3.58 ± 0.28) × 10 -4 and the cluster peculiar velocity v z=-538 ± 414kms -1. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Governato F.,University of Washington | Zolotov A.,Hebrew University of Jerusalem | Pontzen A.,University of Oxford | Christensen C.,33 North Cherry Avenue | And 6 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2012

We examine the evolution of the inner dark matter (DM) and baryonic density profile of a new sample of simulated field galaxies using fully cosmological, Λ cold dark matter (ΛCDM), high-resolution SPH+N-Body simulations. These simulations include explicit H 2 and metal cooling, star formation (SF) and supernovae-driven gas outflows. Starting at high redshift, rapid, repeated gas outflows following bursty SF transfer energy to the DM component and significantly flatten the originally 'cuspy' central DM mass profile of galaxies with present-day stellar masses in the 10 4.5-10 9.8M ⊙ range. At z= 0, the central slope of the DM density profile of our galaxies (measured between 0.3 and 0.7 kpc from their centre) is well fitted by ρ DM∝r α with α≃-0.5 + 0.35 log 10(M */10 8M ⊙), where M * is the stellar mass of the galaxy and 4 < logM * < 9.4. These values imply DM profiles flatter than those obtained in DM-only simulations and in close agreement with those inferred in galaxies from the THINGS and LITTLE THINGS surveys. Only in very small haloes, where by z= 0 SF has converted less than ∼0.03 per cent of the original baryon abundance into stars, outflows do not flatten the original cuspy DM profile out to radii resolved by our simulations. The mass (DM and baryonic) measured within the inner 500pc of each simulated galaxy remains nearly constant over 4 orders of magnitudes in stellar mass for M * < 10 9M ⊙. This finding is consistent with estimates for faint Local Group dwarfs and field galaxies. These results address one of the outstanding problems faced by the CDM model, namely the strong discrepancy between the original predictions of cuspy DM profiles and the shallower central DM distribution observed in galaxies. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Zolotov A.,Hebrew University of Jerusalem | Brooks A.M.,University of Wisconsin - Madison | Willman B.,Haverford College | Governato F.,University of Washington | And 6 more authors.
Astrophysical Journal | Year: 2012

Using high-resolution cosmological hydrodynamical simulations of Milky Way-massed disk galaxies, we demonstrate that supernovae feedback and tidal stripping lower the central masses of bright (-15 < MV < -8) satellite galaxies. These simulations resolve high-density regions, comparable to giant molecular clouds, where stars form. This resolution allows us to adopt a prescription for H2 formation and destruction that ties star formation to the presence of shielded, molecular gas. Before infall, supernova feedback from the clumpy, bursty star formation captured by this physically motivated model leads to reduced dark matter (DM) densities and shallower inner density profiles in the massive satellite progenitors (M vir ≥ 109 M , M * ≥ 107 M ) compared with DM-only simulations. The progenitors of the lower mass satellites are unable to maintain bursty star formation histories, due to both heating at reionization and gas loss from initial star-forming events, preserving the steep inner density profile predicted by DM-only simulations. After infall, gas stripping from satellites reduces the total central masses of satellites simulated with DM+baryons relative to DM-only satellites. Additionally, enhanced tidal stripping after infall due to the baryonic disk acts to further reduce the central DM densities of the luminous satellites. Satellites that enter with cored DM halos are particularly vulnerable to the tidal effects of the disk, exacerbating the discrepancy in the central masses predicted by baryon+DM and DM-only simulations. We show that DM-only simulations, which neglect the highly non-adiabatic evolution of baryons described in this work, produce denser satellites with larger central velocities. We provide a simple correction to the central DM mass predicted for satellites by DM-only simulations. We conclude that DM-only simulations should be used with great caution when interpreting kinematic observations of the Milky Way's dwarf satellites. © 2012. The American Astronomical Society. All rights reserved..

Sheth K.,U.S. National Radio Astronomy Observatory | Melbourne J.,California Institute of Technology | Elmegreen D.M.,Vassar College | Elmegreen B.G.,IBM | And 3 more authors.
Astrophysical Journal | Year: 2012

We present observational evidence for the inhibition of bar formation in dispersion-dominated (dynamically hot) galaxies by studying the relationship between galactic structure and host galaxy kinematics in a sample of 257 galaxies between 0.1 < z ≤ 0.84 from the All-Wavelength Extended Groth Strip International Survey and the Deep Extragalactic Evolutionary Probe 2 survey. We find that bars are preferentially found in galaxies that are massive and dynamically cold (rotation-dominated) and on the stellar Tully-Fisher relationship, as is the case for barred spirals in the local universe. The data provide at least one explanation for the steep (×3) decline in the overall bar fraction from z = 0 to z = 0.84 in L* and brighter disks seen in previous studies. The decline in the bar fraction at high redshift is almost exclusively in the lower mass (10 < log M *(M ⊙) < 11), later-type, and bluer galaxies. A proposed explanation for this "downsizing" of the bar formation/stellar structure formation is that the lower mass galaxies may not form bars because they could be dynamically hotter than more massive systems from the increased turbulence of accreting gas, elevated star formation, and/or increased interaction/merger rate at higher redshifts. The evidence presented here provides observational support for this hypothesis. However, the data also show that not every disk galaxy that is massive and cold has a stellar bar, suggesting that mass and dynamic coldness of a disk are necessary but not sufficient conditions for bar formation - a secondary process, perhaps the interaction history between the dark matter halo and the baryonic matter, may play an important role in bar formation. © 2012. The American Astronomical Society. All rights reserved.

Loading 33 North Cherry Avenue collaborators
Loading 33 North Cherry Avenue collaborators