Ersic Profile Research Articles

Deprojecting Sérsic Profiles for Arbitrary Triaxial Shapes: Robust Measures of Intrinsic and Projected Galaxy Sizes

Abstract We present the analytical framework for converting projected light distributions with a Sérsic profile into three-dimensional light distributions for stellar systems of arbitrary triaxial shape. The main practical result is the definition of a simple yet robust measure of intrinsic galaxy size: the median radius r med, defined as the radius of a sphere that contains 50% of the total luminosity or mass, that is, the median distance of a star to the galaxy center. We examine how r med depends on projected size measurements as a function of Sérsic index and intrinsic axis ratios, and demonstrate its relative independence of these parameters. As an application we show that the projected semimajor axis length of the ellipse enclosing 50% of the light is an unbiased proxy for r med, with small galaxy-to-galaxy scatter of ∼10% (1σ), under the condition that the variation in triaxiality within the population is small. For galaxy populations with an unknown or a large range in triaxiality an unbiased proxy for r med is 1.3 × R e , where R e is the circularized half-light radius, with galaxy-to-galaxy scatter of 20%–30% (1σ). We also describe how inclinations can be estimated for individual galaxies based on the measured projected shape and prior knowledge of the intrinsic shape distribution of the corresponding galaxy population. We make the numerical implementation of our calculations available.

Automated detectionof very low surface brightness galaxiesin the Virgo cluster

We report the automatic detection of a new sample of very low surface brightness (LSB) galaxies, likely members of the Virgo cluster. We introduce our new software, {\tt DeepScan}, that has been designed specifically to detect extended LSB features automatically using the DBSCAN algorithm. We demonstrate the technique by applying it over a 5 degree$^2$ portion of the Next-Generation Virgo Survey (NGVS) data to reveal 53 low surface brightness galaxies that are candidate cluster members based on their sizes and colours. 30 of these sources are new detections despite the region being searched specifically for LSB galaxies previously. Our final sample contains galaxies with $26.0\leq\langle \mu_{e}\rangle\leq28.5$ and $19\leq m_{g}\leq21$, making them some of the faintest known in Virgo. The majority of them have colours consistent with the red sequence, and have a mean stellar mass of $10^{6.3\pm0.5} M_{\odot}$ assuming cluster membership. After using {\tt ProFit} to fit S\'ersic profiles to our detections, none of the new sources have effective radii larger than 1.5 Kpc and do not meet the criteria for ultra-diffuse galaxy (UDG) classification, so we classify them as ultra-faint dwarfs.

Resolving the host galaxy of a distant blazar with LBT/LUCI 1 + ARGOS

BL Lac objects emitting in the Very High Energy (VHE) regime are unique tools to peer into the properties of the Extragalactic Background Light (EBL). However, due to the typical absence of features in their spectra, the determination of their redshifts has proven challenging. In this work we exploit the superb spatial resolution delivered by the new Advanced Rayleigh guided Ground layer adaptive Optics System (ARGOS) at the Large Binocular Telescope to detect the host galaxy of HESS J1943+213, a VHE emitting BL Lac shining through the Galaxy. Deep H-band imaging collected during the ARGOS commissioning allowed us to separate the contribution of the nuclear emission and to unveil the properties of the host galaxy with unprecedented detail. The host galaxy is well fitted by a S\'ersic profile with index of n~2 and total magnitude of H~16.15 mag. Under the assumption that BL Lac host galaxies are standard candles, we infer a redshift of z~0.21. In the framework of the current model for the EBL, this value is in agreement with the observed dimming of the VHE spectrum due to the scatter of energetic photons on the EBL.

The fate of the Antennae galaxies

We present a high-resolution smoothed particle hydrodynamics simulation of the Antennae galaxies (NGC 4038/4039) and follow the evolution $3$ Gyrs beyond the final coalescence. The simulation includes metallicity dependent cooling, star formation, and both stellar feedback and chemical enrichment. The simulated best-match Antennae reproduces well both the observed morphology and the off-nuclear starburst. We also produce for the first time a simulated two-dimensional metallicity map of the Antennae and find good agreement with the observed metallicity of off-nuclear stellar clusters, however the nuclear metallicities are overproduced by $\sim 0.5$ dex. Using the radiative transfer code SKIRT we produce multi-wavelength observations of both the Antennae and the merger remnant. The $1$ Gyr old remnant is well fitted with a S\'ersic profile of $n=7.07$, and with an $r$-band effective radius of $r_{\mathrm{e}}= 1.6$ kpc and velocity dispersion of $\sigma_{\mathrm{e}}=180$ km$/$s the remnant is located on the fundamental plane of early-type galaxies (ETGs). The initially blue Antennae remnant evolves onto the red sequence after $\sim 2.5$ Gyr of secular evolution. The remnant would be classified as a fast rotator, as the specific angular momentum evolves from $\lambda_{\mathrm{Re}}\approx0.11$ to $\lambda_{\mathrm{Re}}\approx0.14$ during its evolution. The remnant shows ordered rotation and a double peaked maximum in the mean 2D line-of-sight velocity. These kinematical features are relatively common among local ETGs and we specifically identify three local ETGs (NGC 3226, NGC 3379 and NGC 4494) in the ATLAS$^\mathrm{3D}$ sample, whose photometric and kinematic properties most resemble the Antennae remnant.

The Herschel-ATLAS: magnifications and physical sizes of 500-μm-selected strongly lensed galaxies

We perform lens modelling and source reconstruction of Submillimeter Array (SMA) data for a sample of 12 strongly lensed galaxies selected at 500$\mu$m in the Herschel Astrophysical Terahertz Large Area Survey H-ATLAS. A previous analysis of the same dataset used a single S\`ersic profile to model the light distribution of each background galaxy. Here we model the source brightness distribution with an adaptive pixel scale scheme, extended to work in the Fourier visibility space of interferometry. We also present new SMA observations for seven other candidate lensed galaxies from the H-ATLAS sample. Our derived lens model parameters are in general consistent with previous findings. However, our estimated magnification factors, ranging from 3 to 10, are lower. The discrepancies are observed in particular where the reconstructed source hints at the presence of multiple knots of emission. We define an effective radius of the reconstructed sources based on the area in the source plane where emission is detected above 5$\sigma$. We also fit the reconstructed source surface brightness with an elliptical Gaussian model. We derive a median value $r_{eff}\,\sim 1.77\,$kpc and a median Gaussian full width at half maximum $\sim1.47\,$kpc. After correction for magnification, our sources have intrinsic star formation rates SFR$\,\sim900-3500\,M_{\odot}yr^{-1}$, resulting in a median star formation rate surface density $\Sigma_{SFR}\sim132\,M_{\odot}$ yr$^{-1}$ kpc$^{-2}$ (or $\sim 218\,M_{\odot}$ yr$^{-1}$ kpc$^{-2}$ for the Gaussian fit). This is consistent with what observed for other star forming galaxies at similar redshifts, and is significantly below the Eddington limit for a radiation pressure regulated starburst.

The VIMOS Public Extragalactic Redshift Survey (VIPERS)

We explore the evolution of the statistical distribution of galaxy morphological properties and colours over the redshift range $0.5<z<1$, combining high-quality imaging data from the CFHT Legacy Survey with the large number of redshifts and extended photometry from the VIPERS survey. Galaxy structural parameters are measured by fitting S\'ersic profiles to $i$-band images and then combined with absolute magnitudes, colours and redshifts, to trace the evolution in a multi-parameter space. We analyse, using a new method, the combination of colours and structural parameters of early- and late-type galaxies in luminosity--redshift space. We found that both the rest-frame colour distributions in the (U-B) vs. (B-V) plane and the S\'ersic index distributions are well fitted by a sum of two Gaussians, with a remarkable consistency of red-spheroidal and blue-disky galaxy populations, over the explored redshift ($0.5<z<1$) and luminosity ($-1.5<B-B_*<1.0$) ranges. The combination of the UBV rest-frame colour and S\'ersic index $n$ as a function of redshift and luminosity allows us to present the structure of early- and late-type galaxies and their evolution. We found that early type galaxies display only a slow change of their concentrations since $z\sim1$; it is already established by $z\sim1$ and depends much more strongly on their luminosities. In contrast, late-type galaxies get clearly more concentrated with cosmic time since $z\sim1$, with only little evolution in colour, which remains dependent mainly on their luminosity. This flipped luminosity (mass) and redshift dependence likely reflects different evolutionary tracks of early- and late-type galaxies before and after $z\sim1$. The combination of rest-frame colours and S\'ersic index $n$ as a function of redshift and luminosity leads to a precise statistical description of the structure of galaxies and their evolution.

The formation of bulges, discs and two-component galaxies in the CANDELS Survey atz &lt; 3

We examine a sample of 1495 galaxies in the CANDELS fields to determine the evolution of two component galaxies, including bulges and discs, within massive galaxies at the epoch 1 < z < 3 when the Hubble sequence forms. We fit all of our galaxies' light profiles with a single S\'ersic fit, as well as with a combination of exponential and S\'ersic profiles. The latter is done in order to describe a galaxy with an inner and an outer component, or bulge and disc component. We develop and use three classification methods (visual, F-test and the RFF) to separate our sample into 1-component galaxies (disc/spheroids-like galaxies) and 2-component galaxies (galaxies formed by an 'inner part' or bulge and an 'outer part' or disc). We then compare the results from using these three different ways to classify our galaxies. We find that the fraction of galaxies selected as 2-component galaxies increases on average 50 per cent from the lowest mass bin to the most massive galaxies, and decreases with redshift by a factor of four from z = 1 to z = 3. We find that single S\'ersic 'disc-like' galaxies have the highest relative number densities at all redshifts, and that 2-component galaxies have the greatest increase and become at par with S\'ersic discs by z = 1. We also find that the systems we classify as 2-component galaxies have an increase in the sizes of their outer components, or 'discs', by about a factor of three from z = 3 to z = 1.5, while the inner components or 'bulges' stay roughly the same size. This suggests that these systems are growing from the inside out, whilst the bulges or protobulges are in place early in the history of these galaxies. This is also seen to a lesser degree in the growth of single 'disc-like' galaxies vs. 'spheroid-like' galaxies over the same epoch.

Non-parametric analysis of the rest-frame UV sizes and morphological disturbance amongstL*galaxies at 4 &lt;z&lt; 8

We present the results of a study investigating the sizes and morphologies of redshift 4 < z < 8 galaxies in the CANDELS GOODS-S, HUDF and HUDF parallel fields. Based on non-parametric measurements and incorporating a careful treatment of measurement biases, we quantify the typical size of galaxies at each redshift as the peak of the log-normal size distribution, rather than the arithmetic mean size. Parameterizing the evolution of galaxy half-light radius as $r_{50} \propto (1+z)^n$, we find $n = -0.20 \pm 0.26$ at bright UV-luminosities ($0.3L_{*(z=3)} < L < L_*$) and $n = -0.47 \pm 0.62$ at faint luminosities ($0.12L_* < L < 0.3L_*$). Furthermore, simulations based on artificially redshifting our z~4 galaxy sample show that we cannot reject the null hypothesis of no size evolution. We show that this result is caused by a combination of the size-dependent completeness of high-redshift galaxy samples and the underestimation of the sizes of the largest galaxies at a given epoch. To explore the evolution of galaxy morphology we first compare asymmetry measurements to those from a large sample of simulated single S\'ersic profiles, in order to robustly categorise galaxies as either `smooth' or `disturbed'. Comparing the disturbed fraction amongst bright ($M_{UV} \leq -20$) galaxies at each redshift to that obtained by artificially redshifting our z~4 galaxy sample, while carefully matching the size and UV-luminosity distributions, we find no clear evidence for evolution in galaxy morphology over the redshift interval 4 < z < 8. Therefore, based on our results, a bright ($M_{UV} \leq -20$) galaxy at z~6 is no more likely to be measured as `disturbed' than a comparable galaxy at z~4, given the current observational constraints.

The SAMI Galaxy Survey: gas streaming and dynamical M/L in rotationally supported systems

Line-of-sight velocities of gas and stars can constrain dark matter (DM) within rotationally supported galaxies if they trace circular orbits extensively. Photometric asymmetries may signify non-circular motions, requiring spectra with dense spatial coverage. Our integral-field spectroscopy of 178 galaxies spanned the mass range of the SAMI Galaxy Survey. We derived circular speed curves (CSCs) of gas and stars from non-parametric Diskfit fits out to $r\sim2r_e$. For 12/14 with measured H I profiles, ionized gas and H I maximum velocities agreed. We fitted mass-follows-light models to 163 galaxies by approximating the radial starlight profile as nested, very flattened mass homeoids viewed as a S\'ersic form. Fitting broad-band SEDs to SDSS images gave median stellar mass/light 1.7 assuming a Kroupa IMF vs. 2.6 dynamically. Two-thirds of the dynamical mass/light measures were consistent with star+remnant IMFs. One-fifth required upscaled starlight to fit, hence comparable mass of unobserved baryons and/or DM distributed similarly across the SAMI aperture that came to dominate motions as the starlight CSC declined rapidly. The rest had mass distributed differently from starlight. Subtracting fits of S\'ersic profiles to 13 VIKING Z-band images revealed residual weak bars. Near the bar PA, we assessed m = 2 streaming velocities, and found deviations usually <30 km/s from the CSC; three showed no deviation. Thus, asymmetries rarely influenced our CSCs despite co-located shock-indicating, emission-line flux ratios in more than 2/3.

THE SIZES OFz∼ 6–8 LENSED GALAXIES FROM THE HUBBLE FRONTIER FIELDS ABELL 2744 DATA

We investigate sizes of $z\sim6-8$ dropout galaxies using the complete data of the Abell 2744 cluster and parallel fields in the Hubble Frontier Fields program. By directly fitting light profiles of observed galaxies with lensing-distorted S\'ersic profiles on the image plane with the \texttt{glafic} software, we accurately measure intrinsic sizes of 31 $z\sim6-7$ and eight $z\sim8$ galaxies, including those as faint as $M_{\mathrm{UV}}\simeq-16.6$. We find that half-light radii $r_\mathrm{e}$ positively correlates with UV luminosity at each redshift, although the correlation is not very tight. Largest ($r_\mathrm{e}>0.8$ kpc) galaxies are mostly red in UV color while smallest ($r_\mathrm{e} < 0.08$ kpc) ones tend to be blue. We also find that galaxies with multiple cores tend to be brighter. Combined with previous results at $2.5\lesssim z\lesssim12$, our result confirms that the average $r_{\mathrm{e}}$ of bright ($(0.3-1)L^\star_{z=3}$) galaxies scales as $r_{\mathrm{e}}\propto(1+z)^{-m}$ with $m=1.24\pm0.1$. We find that the ratio of $r_\mathrm{e}$ to virial radius is virtually constant at $3.3\pm0.1\%$ over a wide redshift range, where the virial radii of hosting dark matter halos are derived based on the abundance matching. This constant ratio is consistent with the disk formation model by Mo et al. (1998) with $j_\mathrm{d}\sim m_\mathrm{d}$, where $j_\mathrm{d}$ and $m_\mathrm{d}$ are the fractions of the angular momentum and mass within halos confined in the disks. A comparison with various types of local galaxies indicates that our galaxies are most similar to circumnuclear star-forming regions of barred galaxies in the sense that a sizable amount of stars are forming in a very small area.

THE SINS/zC-SINF SURVEY OFz∼ 2 GALAXY KINEMATICS: REST-FRAME MORPHOLOGY, STRUCTURE, AND COLORS FROM NEAR-INFRAREDHUBBLE SPACE TELESCOPEIMAGING

We present the analysis of HST $J$- and $H$-band imaging for 29 galaxies on the star-forming main sequence at $z\sim2$, which have Adaptive Optics VLT SINFONI integral field spectroscopy from our SINS/zC-SINF program. The SINFONI H$\alpha$ data resolve the on-going star-formation and the ionized gas kinematics on scales of $1-2$ kpc; the near-IR images trace the galaxies' rest-frame optical morphologies and distributions of stellar mass in old stellar populations at a similar resolution. The global light profiles of most galaxies show disk-like properties well described by a single S\'ersic profile with $n\sim1$, with only $\sim15%$ requiring a high $n>3$ S\'ersic index, all more massive than $10^{10}M_\odot$. In bulge+disk fits, about $40%$ of galaxies have a measurable bulge component in the light profiles, with $\sim15%$ showing a substantial bulge-to-total ratio $B/T\ge0.3$. This is a lower limit to the frequency of $z\sim2$ massive galaxies with a developed bulge component in stellar mass because it could be hidden by dust and/or outshined by a thick actively star-forming disk component. The galaxies' rest-optical half-light radii range between $1-7$ kpc, with a median of 2.1 kpc, and lie slightly above the size-mass relation at these epochs reported in the literature. This is attributed to differences in sample selection and definitions of size and/or mass measurements. The $(u-g)_{rest}$ color gradient and scatter within individual $z\sim2$ massive galaxies with $\ge10^{11}M_\odot$ are as high as in $z=0$ low-mass, late-type galaxies, and are consistent with the high star-formation rates of massive $z\sim2$ galaxies being sustained at large galactocentric distances.

How elevated is the dynamical-to-stellar mass ratio of the ultracompact dwarf S999?

Here we present new Keck ESI high-resolution spectroscopy and deep archival HST/ACS imaging for S999, an ultra-compact dwarf in the vicinity of M87, which was claimed to have an extremely high dynamical-to-stellar mass ratio. Our data increase the total integration times by a factor of 5 and 60 for spectroscopy and imaging, respectively. This allows us to constrain the stellar population parameters for the first time (simple stellar population equivalent age $=7.6^{+2.0}_{-1.6}$ Gyr; $[Z/\textrm{H}]=-0.95^{+0.12}_{-0.10}$; $[\alpha/\textrm{Fe}]=0.34^{+0.10}_{-0.12}$). Assuming a Kroupa stellar initial mass function, the stellar population parameters and luminosity ($M_{F814W}=-12.13\pm0.06$ mag) yield a stellar mass of $M_*=3.9^{+0.9}_{-0.6}\times10^6 M_{\odot}$, which we also find to be consistent with near-infrared data. Via mass modelling, with our new measurements of velocity dispersion ($\sigma_{ap}=27\pm2$ km s$^{-1}$) and size ($R_e=20.9\pm1.0$ pc), we obtain an elevated dynamical-to-stellar mass ratio $M_{dyn}/M_*=8.2$ (with a range $5.6\le M_{dyn}/M_* \le 11.2$). Furthermore, we analyse the surface brightness profile of S999, finding only a small excess of light in the outer parts with respect to the fitted S\'ersic profile, and a positive colour gradient. Taken together these observations suggest that S999 is the remnant of a much larger galaxy that has been tidally stripped. If so, the observed elevated mass ratio may be caused by mechanisms related to the stripping process: the existence of an massive central black hole or internal kinematics that are out of equilibrium due to the stripping event. Given the observed dynamical-to-stellar mass ratio we suggest that S999 is an ideal candidate to search for the presence of an overly massive central black hole.

THE HOST GALAXY OF THE GAMMA-RAY NARROW-LINE SEYFERT 1 GALAXY 1H 0323+342

We present optical and near infrared (NIR) imaging data of the radio-loud Narrow-line Seyfert 1 galaxy 1H 0323+342, which shows intense and variable gamma-ray activity discovered by the Fermi satellite with the Large Area Telescope. NIR and optical images are used to investigate the structural properties of the host galaxy of 1H 0323+342; this together with optical spectroscopy allowed us to examine its black hole mass. Based on the 2D multiwavelength surface brightness modeling, we find that, statistically, the best model fit is a combination of a nuclear component and a S\'ersic profile (n~2.8). However, the presence of a disc component (with a small bulge n~1.2) remains also a possibility and cannot be ruled out with the present data. Although at first glance a spiral-arm like structure is revealed in our images, a 2D Fourier analysis of the imagery suggests that such structure corresponds to an asymmetric ring, likely associated to a recent violent dynamical interaction. We discuss our results on the context of relativistic jets production and galaxy evolution.

EXTENDED STRUCTURE AND FATE OF THE NUCLEUS IN HENIZE 2-10

We investigate the structure and nuclear region of the black hole (BH) hosting galaxy Henize2-10. Surface brightness (SB) profiles are analyzed using Magellan/Megacam $g$- and $r$-band images. Excluding the central starburst, we find a best-fit two component S\'ersic profile with $n_{\rm in} \sim 0.6$, $r_{\text{eff,in}} \sim$ 260~pc, and $n_{\rm out}\sim 1.8$, $r_{\text{eff, out}}\sim$ 1 kpc. Integrating out to our outer most data point (100 arc sec $\sim$ 4.3 kpc), we calculate $M_g=-19.2$ and $M_r=-19.8$. The corresponding enclosed stellar mass is $M_{\star}\sim(10\pm3)\times10^9$ M$_\odot$, $\sim3\times$ larger than previous estimates. Apart from the central $\lesssim$500 pc, with blue colors and an irregular morphology, the galaxy appears to be an early-type system. The outer color is quite red, $(g-r)_0=0.75$, suggesting a dominant old population. We study the nuclear region of the galaxy using archival Gemini/NIFS $K$-band adaptive optics spectroscopy and {\it Hubble Space Telescope} imaging. We place an upper limit on the BH mass of $\sim10^7M_{\odot}$ from the NIFS data, consistent with that from the $M_{\rm BH}$-radio-X-ray fundamental plane. No coronal lines are seen, but a Br$\gamma$ source is located at the position of the BH with a luminosity consistent with the X-ray emission. The starburst at the center of Henize 2-10 has led to the formation of several super star clusters, which are within $\sim$100 pc of the BH. We examine the fate of the nucleus by estimating the dynamical masses and dynamical friction timescales of the clusters. The most massive clusters ($\sim 10^6 M_\odot$) have $\tau_{\rm dyn} \lesssim 200$ Myr, and thus Henize 2-10 may represent a rare snapshot of nuclear star cluster formation around a pre-existing massive BH.

HOW ROBUST ARE THE SIZE MEASUREMENTS OF HIGH-REDSHIFT COMPACT GALAXIES?

Massive quiescent galaxies at $z \approx 2$ are apparently much more compact than galaxies of comparable mass today. How robust are these size measurements? We perform comprehensive simulations to determine possible biases and uncertainties in fitting single-component light distributions to real galaxies. In particular, we examine the robustness of the measurements of the luminosity, size, and other structural parameters. We devise simulations with increasing realism to systematically disentangle effects due to the technique (specifically using GALFIT) and the intrinsic structures of the galaxies. By accurately capturing the detailed substructures of nearby elliptical galaxies and then rescaling their sizes and signal-to-noise to mimic galaxies at different redshifts, we confirm that the massive quiescent galaxies at $z \approx 2$ are significantly more compact intrinsically than their local counterparts. Their observed compactness is not a result of missing faint outer light due to systematic errors in modeling. In fact, we find that fitting multi-component galaxies with a single S\'ersic profile, the procedure most commonly adopted in the literature, biases the inferred sizes higher by up to 10% - 20%, which accentuates the amount of size evolution required. If the sky estimation has been done robustly and the model for the point-spread function is fairly accurate, GALFIT can retrieve the properties of single-component galaxies over a wide range of signal-to-noise ratios without introducing any systematic errors.

The distribution of interstellar dust in CALIFA edge-on galaxies via oligochromatic radiative transfer fitting

We investigate the amount and spatial distribution of interstellar dust in edge-on spiral galaxies, using detailed radiative transfer modeling of a homogeneous sample of 12 galaxies selected from the CALIFA survey. Our automated fitting routine, FitSKIRT, was first validated against artificial data. This is done by simultaneously reproducing the SDSS $g$-, $r$-, $i$- and $z$-band observations of a toy model in order to combine the information present in the different bands. We show that this combined, oligochromatic fitting, has clear advantages over standard monochromatic fitting especially regarding constraints on the dust properties. We model all galaxies in our sample using a three-component model, consisting of a double exponential disc to describe the stellar and dust discs and using a S\'ersic profile to describe the central bulge. The full model contains 19 free parameters, and we are able to constrain all these parameters to a satisfactory level of accuracy without human intervention or strong boundary conditions. Apart from two galaxies, the entire sample can be accurately reproduced by our model. We find that the dust disc is about 75% more extended but only half as high as the stellar disc. The average face-on optical depth in the V-band is $0.76$ and the spread of $0.60$ within our sample is quite substantial, which indicates that some spiral galaxies are relatively opaque even when seen face-on.

THE LYMAN ALPHA REFERENCE SAMPLE. II.HUBBLE SPACE TELESCOPEIMAGING RESULTS, INTEGRATED PROPERTIES, AND TRENDS

We report upon new results regarding the Lya output of galaxies, derived from the Lyman alpha Reference Sample (LARS), focusing on Hubble Space Telescope imaging. For 14 galaxies we present intensity images in Lya, Halpha, and UV, and maps of Halpha/Hbeta, Lya equivalent width (EW), and Lya/Halpha. We present Lya and UV light profiles and show they are well-fitted by S\'ersic profiles, but Lya profiles show indices systematically lower than those of the UV (n approx 1-2 instead of >~4). This reveals a general lack of the central concentration in Lya that is ubiquitous in the UV. Photometric growth curves increase more slowly for Lya than the FUV, showing that small apertures may underestimate the EW. For most galaxies, however, flux and EW curves flatten by radii ~10 kpc, suggesting that if placed at high-z, only a few of our galaxies would suffer from large flux losses. We compute global properties of the sample in large apertures, and show total luminosities to be independent of all other quantities. Normalized Lya throughput, however, shows significant correlations: escape is found to be higher in galaxies of lower star formation rate, dust content, mass, and several quantities that suggest harder ionizing continuum and lower metallicity. Eight galaxies could be selected as high-z Lya emitters, based upon their luminosity and EW. We discuss the results in the context of high-z Lya and UV samples. A few galaxies have EWs above 50 AA, and one shows f_escLya of 80%; such objects have not previously been reported at low-z.

The host galaxy of the z = 2.4 radio-loud AGN MRC 0406−244 as seen by HST

We present multicolour Hubble Space Telescope images of the powerful z=2.4 radio galaxy MRC 0406-244 and model its complex morphology with several components including a host galaxy, a point source, and extended nebular and continuum emission. We suggest that the main progenitor of this radio galaxy was a normal, albeit massive (M ~10^{11} solar masses), star-forming galaxy. The optical stellar disc of the host galaxy is smooth and well described by a S\'ersic profile, which argues against a recent major merger, however there is also a point-source component which may be the remnant of a minor merger. The half-light radius of the optical disc is constrained to lie in the range 3.5 to 8.2kpc, which is of similar size to coeval star forming galaxies. Biconical shells of nebular emission and UV-bright continuum extend out from the host galaxy along the radio jet axis, which is also the minor axis of the host galaxy. The origin of the continuum emission is uncertain, but it is most likely to be young stars or dust-scattered light from the AGN, and it is possible that stars are forming from this material at a rate of 200^{+1420}_{-110} solar masses per year.

MegaMorph – multiwavelength measurement of galaxy structure. Sérsic profile fits to galaxies near and far

We demonstrate a new multi-wavelength technique for two-dimensional parametric modelling of galaxy surface-brightness profiles, which we have incorporated into the widely used software GALFIT. Our new method, named GALFITM, extends GALFIT3's current single-band fitting process by simultaneously using multiple images of the same galaxy to constrain a wavelength-dependent model. Each standard profile parameter may vary as a function of wavelength, with a user-definable degree of smoothness, from constant to fully free. The performance of GALFITM is evaluated by fitting elliptical S\'ersic profiles to ugriz imaging data for 4026 galaxies, comprising the original SDSS imaging for 163 low redshift (v < 7000 kms) galaxies and 3863 artificially redshifted (0.01 < z < 0.25) images of the same galaxies. Comparing results from single-band and multi-band techniques, we show that GALFITM significantly improves the extraction of information, particularly from bands with low signal-to-noise ratio (e.g., u and z SDSS bands) when combined with higher signal-to-noise images. We also study systematic trends in the recovered parameters, particularly S\'ersic index, that appear when one performs measurements of the same galaxies at successively higher redshifts. We argue that it is vital that studies investigating the evolution of galaxy structure are careful to avoid or correct for these biases. The resulting multi-band photometric structural parameters for our sample of 163 galaxies are provided. We demonstrate the importance of considering multi-band measurements by showing that the S\'ersic indices of spiral galaxies increase to redder wavelengths, as expected for composite bulge-disk systems. Finally, for the ellipticals in our sample, which should be well-represented by single-S\'ersic models, we compare our measured parameters to those from previous studies.

DA WHITE DWARFS OBSERVED IN THE LAMOST PILOT SURVEY

A total of $\sim640,000$ objects from LAMOST pilot survey have been publicly released. In this work, we present a catalog of DA white dwarfs from the entire pilot survey. We outline a new algorithm for the selection of white dwarfs by fitting S\'ersic profiles to the Balmer H$\beta$, H$\gamma$ and H$\delta$ lines of the spectra, and calculating the equivalent width of the CaII K line. 2964 candidates are selected by constraining the fitting parameters and the equivalent width of CaII K line. All the spectra of candidates are visually inspected. We identify 230 (59 of them are already in Villanova and SDSS WD catalog) DA white dwarfs, 20 of which are DA white dwarfs with non-degenerate companions. In addition, 128 candidates are classified as DA white dwarf/subdwarfs, which means the classifications are ambiguous. The result is consistent with the expected DA white dwarf number estimated based on the LEGUE target selection algorithm.