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Register a new userA subarcsecond near-infrared view of massive galaxies at z > 1 with Gemini Multiconjugate Adaptive Optics
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M. Lacy
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We present images taken using the Gemini South Adaptive Optics Imager (GSAOI) with the Gemini Multiconjugate Adaptive Optics System (GeMS) in three 2 arcmin$^2$ fields in the Spitzer Extragalactic Representative Volume Survey. These GeMS/GSAOI observations are among the first $approx 0.1^{}$ resolution data in the near-infrared spanning extragalactic fields exceeding $1.5^{prime}$ in size. We use these data to estimate galaxy sizes, obtaining results similar to those from studies with the Hubble Space Telescope, though we find a higher fraction of compact star forming galaxies at $z>2$. To disentangle the star-forming galaxies from active galactic nuclei (AGN), we use multiwavelength data from surveys in the optical and infrared, including far-infrared data from Herschel, as well as new radio continuum data from the Australia Telescope Compact Array and Very Large Array. We identify ultraluminous infrared galaxies (ULIRGs) at $z sim 1-3$, which consist of a combination of pure starburst galaxies and Active Galactic Nuclei (AGN)/starburst composites. The ULIRGs show signs of recent merger activity, such as highly disturbed morphologies and include a rare candidate triple AGN. We find that AGN tend to reside in hosts with smaller scale sizes than purely star-forming galaxies of similar infrared luminosity. Our observations demonstrate the potential for MCAO to complement the deeper galaxy surveys to be made with the James Webb Space Telescope.
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Astrometry was not a science case of the Gemini Multiconjugate adaptive optics System (GeMS) at its design stage. However, since GeMS has been in regular science operation with the Gemini South Adaptive Optics Imager (GSAOI), their astrometric performances have been deeply analysed. The non-linear component of the distortion map model shows a characteristic pattern which is similarly repeated in each detector of GSAOI. The nature of this pattern was unknown and subjected to different hypotheses. This paper describes the origin of the GeMS distortion pattern as well as its multi-epoch variation. At the end, it is showed a comparison with the current design of the Multiconjugate Adaptive Optics RelaY (MAORY) of the Extremely Large Telescope (ELT).
Since the year 2000, adaptive optics (AO) has seen the emergence of a variety of new concepts addressing particular science needs; multiconjugate adaptive optics (MCAO) is one of them. By correcting the atmospheric turbulence in 3D using several wavefront sensors and a tomographic phase reconstruction approach, MCAO aims to provide uniform diffraction limited images in the near-infrared over fields of view larger than 1 arcmin square, i.e., 10 to 20 times larger in area than classical single conjugated AO. In this review, we give a brief reminder of the AO principles and limitations, and then focus on aspects particular to MCAO, such as tomography and specific MCAO error sources. We present examples and results from past or current systems: MAD (Multiconjugate Adaptive Optics Demonstrator) and GeMS (Gemini MCAO System) for nighttime astronomy and the AO system, at Big Bear for solar astronomy. We examine MCAO performance (Strehl ratio up to 40percent in H band and full width at half maximum down to 52 mas in the case of MCAO), with a particular focus on photometric and astrometric accuracy, and conclude with considerations on the future of MCAO in the Extremely Large Telescope and post-HST era.
We present the results of a pilot near-infrared (NIR) spectroscopic campaign of five very massive galaxies ($log(text{M}_star/text{M}_odot)>11.45$) in the range of $1.7<z<2.7$. We measure an absorption feature redshift for one galaxy at $z_text{spec}=2.000pm0.006$. For the remaining galaxies, we combine the photometry with the continuum from the spectra to estimate continuum redshifts and stellar population properties. We define a continuum redshift ($z_{rm cont}$ ) as one in which the redshift is estimated probabilistically using EAZY from the combination of catalog photometry and the observed spectrum. We derive the uncertainties on the stellar population synthesis properties using a Monte Carlo simulation and examine the correlations between the parameters with and without the use of the spectrum in the modeling of the spectral energy distributions (SEDs). The spectroscopic constraints confirm the extreme stellar masses of the galaxies in our sample. We find that three out of five galaxies are quiescent (star formation rate of $lesssim 1 M_odot~yr^{-1}$) with low levels of dust obscuration ($A_{rm V} < 1$) , that one galaxy displays both high levels of star formation and dust obscuration (${rm SFR} approx 300 M_odot~{rm yr}^{-1}$, $A_{rm V} approx 1.7$~mag), and that the remaining galaxy has properties that are intermediate between the quiescent and star-forming populations.
We present the stellar mass - size relation for 49 galaxies within the $z$ = 1.067 cluster SPT-CL J0546$-$5345, with FWHM $sim$80-120 mas $K_{mathrm s}$-band data from the Gemini multi-conjugate adaptive optics system (GeMS/GSAOI). This is the first such measurement in a cluster environment, performed at sub-kpc resolution at rest-frame wavelengths dominated by the light of the underlying old stellar populations. The observed stellar mass - size relation is offset from the local relation by 0.21 dex, corresponding to a size evolution proportional to $(1+z)^{-1.25}$, consistent with the literature. The slope of the stellar mass - size relation $beta$ = 0.74 $pm$ 0.06, consistent with the local relation. The absence of slope evolution indicates that the amount of size growth is constant with stellar mass. This suggests that galaxies in massive clusters such as SPT-CL J0546$-$5345 grow via processes that increase the size without significant morphological interference, such as minor mergers and/or adiabatic expansion. The slope of the cluster stellar mass - size relation is significantly shallower if measured in $HST$/ACS imaging at wavelengths blueward of the Balmer break, similar to rest-frame UV relations at $z$ = 1 in the literature. The stellar mass - size relation must be measured at redder wavelengths, which are more sensitive to the old stellar population that dominates the stellar mass of the galaxies. The slope is unchanged when GeMS $K_s$-band imaging is degraded to the resolution of $K$-band HST/NICMOS resolution but dramatically affected when degraded to $K_s$-band Magellan/FourStar resolution. Such measurements must be made with AO in order to accurately characterise the sizes of compact, $z$ = 1 galaxies.
I discuss constraints on star--formation and AGN activity in massive galaxies at z~1-3 using observations from the Spitzer Space Telescope. In particular I focus on a sample of distant red galaxies (DRGs) with J-K>2.3 in GOODS-S. Based on their ACS, ISAAC, and IRAC photometry, the DRGs have typical stellar masses >10^11 Msol. Interestingly, the majority (>50%) of these objects have 24 micron detections. If attributed to star formation, this implies SFRs of ~100-1000 Msol/yr. Thus, massive galaxies at z~1.5-3 have specific SFRs equal to or exceeding the global average value at that epoch. In contrast, galaxies with >10^11 Msol at z~0.3-0.75 have specific SFRs less than the global average, and more than an order of magnitude lower than that at z~1.5-3. Thus, the bulk of assembly of massive galaxies is largely complete by z~1.5. At the same time, based on the X-ray luminosities and near-IR colors, as many as 25% of the massive galaxies at z>1.5 host AGN, implying that the growth of supermassive black holes coincides with massive-galaxy assembly. The analysis of high-redshift galaxies depends on bolometric corrections between the observed 24 micron data and total IR luminosity. I review some of the sources of the (significant) uncertainties on these corrections, and discuss improvements for the future.
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