We present Hubble Space Telescope and simultaneous Swift X-ray telescope observations of the stro... more We present Hubble Space Telescope and simultaneous Swift X-ray telescope observations of the strongest candidate intermediate mass black hole (IMBH) ESO 243-49 HLX-1. Fitting the spectral energy distribution from X-ray to near-infrared wavelengths showed that the broadband spectrum is not consistent with simple and irradiated disc models, but is well described by a model comprised of an irradiated accretion disc plus a ∼10 6 M ⊙ stellar population. The age of the population cannot be uniquely constrained, with both young and old stellar populations allowed. However, the old solution requires excessive disc reprocessing and an extremely small disc, so we favour the young solution (∼13 Myr). In addition, the presence of dust lanes and the lack of any nuclear activity from X-ray observations of the host galaxy suggest that a gas-rich minor merger may have taken place less than ∼200 Myr ago. Such a merger event would explain the presence of the IMBH and the young stellar population.
Monthly Notices of the Royal Astronomical Society, 2013
We calculate stellar masses for ∼ 400, 000 massive luminous galaxies at redshift ∼ 0.2 − 0.7 usin... more We calculate stellar masses for ∼ 400, 000 massive luminous galaxies at redshift ∼ 0.2 − 0.7 using the first two years of data from the Baryon Oscillation Spectroscopic Survey (BOSS). Stellar masses are obtained by fitting model spectral energy distributions to u, g, r, i, z magnitudes. Accurate BOSS spectroscopic redshifts are used to constrain the fits. We find that the distribution of stellar masses in BOSS is narrow (∆ log M ∼ 0.5 dex) and peaks at about log M/M ⊙ ∼ 11.3 (for a Kroupa initial stellar mass function), and that the mass sampling is uniform over the redshift range 0.2 to 0.6, in agreement with the intended BOSS target selection. The galaxy masses probed by BOSS extend over ∼ 10 12 M ⊙ , providing unprecedented measurements of the high-mass end of the galaxy mass function. We find that the galaxy number density above ∼ 2.5 · 10 11 M ⊙ agrees with previous determinations within 2σ, but there is a slight offset towards lower number densities in BOSS. This alleviates a tension between the z ∼ < 0.1 and the high-redshift mass function. We perform a comparison with semi-analytic galaxy formation models tailored to the BOSS target selection and volume, in order to contain incompleteness. The abundance of massive galaxies in the models compare well with the BOSS data. However, no evolution is detected from redshift ∼ 0.6 to 0 in the data, whereas the abundance of massive galaxies in the models increases to redshift zero. BOSS data display colour-magnitude (mass) relations similar to those found in the local Universe, where the most massive galaxies are the reddest. On the other hand, the model colours do not display a dependence on stellar mass, span a narrower range and are typically bluer than the observations. We argue that the lack of a colour-mass relation in the models is mostly due to metallicity, which is too low in the models.
Abstract: We perform a spectroscopic analysis of 492,450 galaxy spectra from the first two years ... more Abstract: We perform a spectroscopic analysis of 492,450 galaxy spectra from the first two years of observations of the Sloan Digital Sky Survey-III/Baryonic Oscillation Spectroscopic Survey (BOSS) collaboration. This data set is released in the ninth SDSS data release in July 2012, the first public data release of BOSS spectra. We show that the typical signal-to-noise ratio of BOSS spectra, despite being low, is sufficient to measure stellar velocity dispersion and emission line fluxes for individual objects. We show that the typical velocity ...
Publications of the Astronomical Society of the Pacific, Jul 1, 2012
ABSTRACT. We present the Spitzer Extragalactic Representative Volume Survey (SERVS), an 18 deg2 1... more ABSTRACT. We present the Spitzer Extragalactic Representative Volume Survey (SERVS), an 18 deg2 18     deg 2 medium-deep survey at 3.6 and 4.5 μm with the postcryogenic Spitzer Space Telescope to≈ 2 μJy≈ 2     μ Jy (AB= 23.1 AB= 23.1) depth of five highly observed astronomical fields (ELAIS-N1, ELAIS-S1, Lockman Hole, Chandra Deep Field South, and XMM-LSS). SERVS is designed to enable the study of galaxy evolution as a function of environment from z~ 5 z~ 5 to the present ...
We combine HST /WFC3 imaging and G141 grism observations from the CANDELS and 3D-HST surveys to p... more We combine HST /WFC3 imaging and G141 grism observations from the CANDELS and 3D-HST surveys to produce a catalog of grism spectroscopic redshifts for galaxies in the CANDELS/GOODS-South field. The WFC3/G141 grism spectra cover a wavelength range of 1.1 ≤ λ ≤ 1.7µm with a resolving power of R ∼ 130 for point sources, thus providing rest-frame optical spectra for galaxies out to z ∼ 3.5. The catalog is selected in the H -band (F160W) and includes both galaxies with and without previously published spectroscopic redshifts. Grism spectra are extracted for all H -band detected galaxies with H≤24 and a CANDELS photometric redshift z phot ≥ 0.6. The resulting spectra are visually inspected to identify emission lines and redshifts are determined using cross-correlation with empirical spectral templates. To establish the accuracy of our redshifts, we compare our results against high-quality spectroscopic redshifts from the literature. Using a sample of 411 control galaxies, this analysis yields a precision of σ N MAD = 0.0028 for the grism-derived redshifts, which is consistent with the accuracy reported by the 3D-HST team. Our final catalog covers an area of 153 arcmin 2 and contains 1019 redshifts for galaxies in GOODS-S. Roughly 60% (608/1019) of these redshifts are for galaxies with no previously published spectroscopic redshift. These new redshifts span a range of 0.677 ≤ z ≤ 3.456 and have a median redshift of z = 1.282. The catalog contains a total of 234 new redshifts for galaxies at z > 1.5. In addition, we present 20 galaxy pair candidates identified for the first time using the grism redshifts in our catalog, including four new galaxy pairs at z ∼ 2, nearly doubling the number of such pairs previously identified.
We present Hubble Space Telescope and simultaneous Swift X-ray telescope observations of the stro... more We present Hubble Space Telescope and simultaneous Swift X-ray telescope observations of the strongest candidate intermediate mass black hole (IMBH) ESO 243-49 HLX-1. Fitting the spectral energy distribution from X-ray to near-infrared wavelengths showed that the broadband spectrum is not consistent with simple and irradiated disc models, but is well described by a model comprised of an irradiated accretion disc plus a ∼10 6 M ⊙ stellar population. The age of the population cannot be uniquely constrained, with both young and old stellar populations allowed. However, the old solution requires excessive disc reprocessing and an extremely small disc, so we favour the young solution (∼13 Myr). In addition, the presence of dust lanes and the lack of any nuclear activity from X-ray observations of the host galaxy suggest that a gas-rich minor merger may have taken place less than ∼200 Myr ago. Such a merger event would explain the presence of the IMBH and the young stellar population.
Monthly Notices of the Royal Astronomical Society, 2013
We calculate stellar masses for ∼ 400, 000 massive luminous galaxies at redshift ∼ 0.2 − 0.7 usin... more We calculate stellar masses for ∼ 400, 000 massive luminous galaxies at redshift ∼ 0.2 − 0.7 using the first two years of data from the Baryon Oscillation Spectroscopic Survey (BOSS). Stellar masses are obtained by fitting model spectral energy distributions to u, g, r, i, z magnitudes. Accurate BOSS spectroscopic redshifts are used to constrain the fits. We find that the distribution of stellar masses in BOSS is narrow (∆ log M ∼ 0.5 dex) and peaks at about log M/M ⊙ ∼ 11.3 (for a Kroupa initial stellar mass function), and that the mass sampling is uniform over the redshift range 0.2 to 0.6, in agreement with the intended BOSS target selection. The galaxy masses probed by BOSS extend over ∼ 10 12 M ⊙ , providing unprecedented measurements of the high-mass end of the galaxy mass function. We find that the galaxy number density above ∼ 2.5 · 10 11 M ⊙ agrees with previous determinations within 2σ, but there is a slight offset towards lower number densities in BOSS. This alleviates a tension between the z ∼ < 0.1 and the high-redshift mass function. We perform a comparison with semi-analytic galaxy formation models tailored to the BOSS target selection and volume, in order to contain incompleteness. The abundance of massive galaxies in the models compare well with the BOSS data. However, no evolution is detected from redshift ∼ 0.6 to 0 in the data, whereas the abundance of massive galaxies in the models increases to redshift zero. BOSS data display colour-magnitude (mass) relations similar to those found in the local Universe, where the most massive galaxies are the reddest. On the other hand, the model colours do not display a dependence on stellar mass, span a narrower range and are typically bluer than the observations. We argue that the lack of a colour-mass relation in the models is mostly due to metallicity, which is too low in the models.
Abstract: We perform a spectroscopic analysis of 492,450 galaxy spectra from the first two years ... more Abstract: We perform a spectroscopic analysis of 492,450 galaxy spectra from the first two years of observations of the Sloan Digital Sky Survey-III/Baryonic Oscillation Spectroscopic Survey (BOSS) collaboration. This data set is released in the ninth SDSS data release in July 2012, the first public data release of BOSS spectra. We show that the typical signal-to-noise ratio of BOSS spectra, despite being low, is sufficient to measure stellar velocity dispersion and emission line fluxes for individual objects. We show that the typical velocity ...
Publications of the Astronomical Society of the Pacific, Jul 1, 2012
ABSTRACT. We present the Spitzer Extragalactic Representative Volume Survey (SERVS), an 18 deg2 1... more ABSTRACT. We present the Spitzer Extragalactic Representative Volume Survey (SERVS), an 18 deg2 18     deg 2 medium-deep survey at 3.6 and 4.5 μm with the postcryogenic Spitzer Space Telescope to≈ 2 μJy≈ 2     μ Jy (AB= 23.1 AB= 23.1) depth of five highly observed astronomical fields (ELAIS-N1, ELAIS-S1, Lockman Hole, Chandra Deep Field South, and XMM-LSS). SERVS is designed to enable the study of galaxy evolution as a function of environment from z~ 5 z~ 5 to the present ...
We combine HST /WFC3 imaging and G141 grism observations from the CANDELS and 3D-HST surveys to p... more We combine HST /WFC3 imaging and G141 grism observations from the CANDELS and 3D-HST surveys to produce a catalog of grism spectroscopic redshifts for galaxies in the CANDELS/GOODS-South field. The WFC3/G141 grism spectra cover a wavelength range of 1.1 ≤ λ ≤ 1.7µm with a resolving power of R ∼ 130 for point sources, thus providing rest-frame optical spectra for galaxies out to z ∼ 3.5. The catalog is selected in the H -band (F160W) and includes both galaxies with and without previously published spectroscopic redshifts. Grism spectra are extracted for all H -band detected galaxies with H≤24 and a CANDELS photometric redshift z phot ≥ 0.6. The resulting spectra are visually inspected to identify emission lines and redshifts are determined using cross-correlation with empirical spectral templates. To establish the accuracy of our redshifts, we compare our results against high-quality spectroscopic redshifts from the literature. Using a sample of 411 control galaxies, this analysis yields a precision of σ N MAD = 0.0028 for the grism-derived redshifts, which is consistent with the accuracy reported by the 3D-HST team. Our final catalog covers an area of 153 arcmin 2 and contains 1019 redshifts for galaxies in GOODS-S. Roughly 60% (608/1019) of these redshifts are for galaxies with no previously published spectroscopic redshift. These new redshifts span a range of 0.677 ≤ z ≤ 3.456 and have a median redshift of z = 1.282. The catalog contains a total of 234 new redshifts for galaxies at z > 1.5. In addition, we present 20 galaxy pair candidates identified for the first time using the grism redshifts in our catalog, including four new galaxy pairs at z ∼ 2, nearly doubling the number of such pairs previously identified.
Uploads
Papers by J. Pforr