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Register a new userSubaru FOCAS IFU observations of two z=0.12 strong-lensing elliptical galaxies from SDSS MaNGA
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We present new observations of two z=0.12 strong-lensing elliptical galaxies, originally discovered from the SDSS-IV MaNGA survey, using the new FOCAS IFU spectrograph on the Subaru Telescope. For J1436+4943, our observations confirm the identification of this system as a multiple-image lens, in a cusp configuration, with Einstein radius $theta_{Ein}$=2.0 arcsec. For J1701+3722, the improved data confirm earlier hints of a complex source plane, with different configurations evident in different emission lines. The new observations reveal a previously unseen inner counter-image to the [OIII] arc found from MaNGA, leading to a smaller revised Einstein radius of $theta_{Ein}$=1.6 arcsec. The inferred projected masses within the Einstein apertures (3.7-4.7kpc) are consistent with being dominated by stars with an initial mass function (IMF) similar to that of the Milky Way, and a dark matter contribution of ~35 per cent as supported from cosmological simulations. These results are consistent with `pure lensing analyses of lower-redshift lenses, but contrast with claims for heavier IMFs from combined lensing-and-dynamical studies of more distant early-type galaxies.
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I report discovery of a new galaxy-scale gravitational lens system, identified using public data from the MaNGA survey, as part of a systematic search for lensed background line-emitters. The lens is SDSS J170124.01+372258.0, a giant elliptical galaxy with velocity dispersion $sigma=256$ km/s, at a redshift of $z_l=0.122$. After modelling and subtracting the target galaxy light, the integral-field data-cube reveals [OII], [OIII] and H$beta$ emission lines corresponding to a source at $z_s=0.791$, forming an identifiable ring around the galaxy center. The Einstein radius is $R_{Ein} approx 2.3$ arcsec, projecting to ~5 kpc at the distance of the lens. The total projected lensing mass is $(3.6pm0.6) times 10^{11} M_odot$, and the total J-band mass-to-light ratio is $3.0pm0.7$ solar units. Plausible estimates of the likely dark matter content could reconcile this with a Milky-Way-like initial mass function (for which M/L~1.5 is expected), but heavier IMFs are by no means excluded with the present data. An alternative interpretation of the system, with a more complex source plane, is also discussed. The discovery of this system bodes well for future lens searches based on MaNGA and other integral-field spectroscopic surveys.
We have conducted a study of extra-planar diffuse ionized gas using the first year data from the MaNGA IFU survey. We have stacked spectra from 49 edge-on, late-type galaxies as a function of distance from the midplane of the galaxy. With this technique we can detect the bright emission lines Halpha, Hbeta, [OII]3726, 3729, [OIII]5007, [NII]6549, 6584, and [SII]6717, 6731 out to about 4 kpc above the midplane. With 16 galaxies we can extend this analysis out to about 9 kpc, i.e. a distance of ~2R_e, vertically from the midplane. In the halo, the surface brightnesses of the [OII] and Halpha emission lines are comparable, unlike in the disk where Halpha dominates. When we split the sample by specific star formation rate, concentration index, and stellar mass, each subsamples emission line surface brightness profiles and ratios differ, indicating that extra-planar gas properties can vary. The emission line surface brightnesses of the gas around high specific star formation rate galaxies are higher at all distances, and the line ratios are closer to ratios characteristic of HII regions compared with low specific star formation rate galaxies. The less concentrated and lower stellar mass samples exhibit line ratios that are more like HII regions at larger distances than their more concentrated and higher stellar mass counterparts. The largest difference between different subsamples occurs when the galaxies are split by stellar mass. We additionally infer that gas far from the midplane in more massive galaxies has the highest temperatures and steepest radial temperature gradients based on their [NII]/Halpha and [OII]/Halpha ratios between the disk and the halo.
We analyse newly obtained Hubble Space Telescope (HST) imaging for two nearby strong lensing elliptical galaxies, SNL-1 (z = 0.03) and SNL-2 (z = 0.05), in order to improve the lensing mass constraints. The imaging reveals previously unseen structure in both the lens galaxies and lensed images. For SNL-1 which has a well resolved source, we break the mass-vs-shear degeneracy using the relative magnification information, and measure a lensing mass of 9.49 $pm$ 0.15 $times$ 10$^{10}$ M$_{odot}$, a 7 per cent increase on the previous estimate. For SNL-2 the imaging reveals a bright unresolved component to the source and this presents additional complexity due to possible AGN microlensing or variability. We tentatively use the relative magnification information to constrain the contribution from SNL-2s nearby companion galaxy, measuring a lensing mass of 12.59 $pm$ 0.30 $times$ 10$^{10}$ M$_{odot}$, a 9 per cent increase in mass. Our improved lens modelling reduces the mass uncertainty from 5 and 10 per cent to 2 and 3 per cent respectively. Our results support the conclusions of the previous analysis, with newly measured mass excess parameters of 1.17 $pm$ 0.09 and 0.96 $pm$ 0.10 for SNL-1 and SNL-2, relative to a Milky-Way like (Kroupa) initial mass function.
We present spectra of high-redshift supernovae (SNe) that were taken with the Subaru low resolution optical spectrograph, FOCAS. These SNe were found in SN surveys with Suprime-Cam on Subaru, the CFH12k camera on the Canada-France-Hawaii Telescope (CFHT), and the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST). These SN surveys specifically targeted z>1 Type Ia supernovae (SNe Ia). From the spectra of 39 candidates, we obtain redshifts for 32 candidates and spectroscopically identify 7 active candidates as probable SNe Ia, including one at z=1.35, which is the most distant SN Ia to be spectroscopically confirmed with a ground-based telescope. An additional 4 candidates are identified as likely SNe Ia from the spectrophotometric properties of their host galaxies. Seven candidates are not SNe Ia, either being SNe of another type or active galactic nuclei. When SNe Ia are observed within a week of maximum light, we find that we can spectroscopically identify most of them up to z=1.1. Beyond this redshift, very few candidates were spectroscopically identified as SNe Ia. The current generation of super red-sensitive, fringe-free CCDs will push this redshift limit higher.
We discuss constraints on the mass density distribution (parameterized as $rhopropto r^{-gamma}$) in early-type galaxies provided by strong lensing and stellar kinematics data. The constraints come from mass measurements at two `pinch radii. One `pinch radius $r_1=2.2 R_{Einst}$ is defined such that the Einstein (i.e. aperture) mass can be converted to the spherical mass almost independently of the mass-model. Another `pinch radius $r_2=R_{opt}$ is chosen so that the dynamical mass, derived from the line-of-sight velocity dispersion, is least sensitive to the anisotropy of stellar orbits. We verified the performance of this approach on a sample of simulated elliptical galaxies and on a sample of 15 SLACS lens galaxies at $0.01 leq z leq 0.35$, which have already been analysed in Barnabe et al. (2011) by the self-consistent joint lensing and kinematic code. For massive simulated galaxies the density slope $gamma$ is recovered with an accuracy of $sim 13%$, unless $r_1$ and $r_2$ happen to be close to each other. For SLACS galaxies, we found good overall agreement with the results of Barnabe et al. (2011) with a sample-averaged slope $gamma=2.1pm0.05$. While the two-pinch-radii approach has larger statistical uncertainties, it is much simpler and uses only few arithmetic operations with directly observable quantities.
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