arXiv subjects

Adi Zitrin

Publications and source records attributed to Adi Zitrin.

244 records · Page 14Linked to original sources

arXiv2010

Full Lensing Analysis of Abell 1703: Comparison of Independent Lens-Modelling Techniques

The inner mass-profile of the relaxed cluster Abell 1703 is analysed by two very different strong-lensing techniques applied to deep ACS and WFC3 imaging. Our parametric method has the accuracy required to reproduce the many sets of multiple images, based on the assumption that mass approximately traces light. We test this assumption with a fully non-parametric, adaptive grid method, with no knowledge of the galaxy distribution. Differences between the methods are seen on fine scales due to member galaxies which must be included in models designed to search for lensed images, but on the larger scale the general distribution of dark matter is in good agreement, with very similar radial mass profiles. We add undiluted weak-lensing measurements from deep multi-colour Subaru imaging to obtain a fully model-independent mass profile out to the virial radius and beyond. Consistency is found in the region of overlap between the weak and strong lensing, and the full mass profile is well-described by an NFW model of a concentration parameter, $c_{\rm vir}\simeq 7.15\pm0.5$ (and $M_{vir}\simeq 1.22\pm0.15 \times 10^{15}M_{\odot}/h$). Abell 1703 lies above the standard $c$--$M$ relation predicted for the standard $Λ$CDM model, similar to other massive relaxed clusters with accurately determined lensing-based profiles.

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arXiv2010

Strong-Lensing Analysis of a Complete Sample of 12 MACS Clusters at z>0.5: Mass Models and Einstein Radii

We present the results of a strong-lensing analysis of a complete sample of 12 very luminous X-ray clusters at $z>0.5$ using HST/ACS images. Our modelling technique has uncovered some of the largest known critical curves outlined by many accurately-predicted sets of multiple images. The distribution of Einstein radii has a median value of $\simeq28\arcsec$ (for a source redshift of $z_{s}\sim2$), twice as large as other lower-$z$ samples, and extends to $55\arcsec$ for MACS J0717.5+3745, with an impressive enclosed Einstein mass of $7.4\times10^{14} M_{\odot}$. We find that 9 clusters cover a very large area ($>2.5 \sq \arcmin$) of high magnification ($μ> \times10$) for a source redshift of $z_{s}\sim8$, providing primary targets for accessing the first stars and galaxies. We compare our results with theoretical predictions of the standard $Λ$CDM model which we show systematically fall short of our measured Einstein radii by a factor of $\simeq1.4$, after accounting for the effect of lensing projection. Nevertheless, a revised analysis once arc redshifts become available, and similar analyses of larger samples, are needed in order to establish more precisely the level of discrepancy with $Λ$CDM predictions.

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arXiv2010

Finding high-redshift dark stars with the James Webb Space Telescope

The first stars in the history of the Universe are likely to form in the dense central regions of 10^5-10^6 Msolar cold dark matter halos at z=10-50. The annihilation of dark matter particles in these environments may lead to the formation of so-called dark stars, which are predicted to be cooler, larger, more massive and potentially more long-lived than conventional population III stars. Here, we investigate the prospects of detecting high-redshift dark stars with the upcoming James Webb Space Telescope (JWST). We find that dark stars at z>6 are intrinsically too faint to be detected by JWST. However, by exploiting foreground galaxy clusters as gravitational telescopes, certain varieties of cool (Teff < 30000 K) dark stars should be within reach at redshifts up to z=10. If the lifetimes of dark stars are sufficiently long, many such objects may also congregate inside the first galaxies. We demonstrate that this could give rise to peculiar features in the integrated spectra of galaxies at high redshifts, provided that dark stars make up at least 1 percent of the total stellar mass in such objects.

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arXiv2010

The Mass Structure of the Galaxy Cluster Cl0024+1654 from a Full Lensing Analysis of Joint Subaru and ACS/NIC3 Observations

We derive an accurate mass distribution of the rich galaxy cluster Cl0024+1654 (z=0.395) based on deep Subaru BR_{c}z' imaging and our recent comprehensive strong lensing analysis of HST/ACS/NIC3 observations. We obtain the weak lensing distortion and magnification of undilted samples of red and blue background galaxies by carefully combining all color and positional information. Unlike previous work, the weak and strong lensing are in excellent agreement where the data overlap. The joint mass profile continuously steepens out to the virial radius with only a minor contribution \sim 10% in the mass from known subcluster at a projected distance of \sim 700kpc/h. The projected mass distribution for the entire cluster is well fitted with a single Navarro-Frenk-White model with a virial mass, M_{vir} = (1.2 \pm 0.2) \times 10^{15} M_{sun}/h, and a concentration, c_{vir} = 9.2^{+1.4}_{-1.2}. This model fit is fully consistent with the depletion of the red background counts, providing independent confirmation. Careful examination and interpretation of X-ray and dynamical data strongly suggest that this cluster system is in a post collision state, which we show is consistent with our well-defined mass profile for a major merger occurring along the line of sight, viewed approximately 2-3Gyr after impact when the gravitational potential has had time to relax in the center, before the gas has recovered and before the outskirts are fully virialized. Finally, our full lensing analysis provides a model-independent constraint of M_{2D}(<r_{vir}) = (1.4 \pm 0.3) \times 10^{15} M_{sun}/h for the projected mass of the whole system, including any currently unbound material beyond the virial radius, which can constrain the sum of the two pre-merger cluster masses when designing simulations to explore this system.

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arXiv2009

The Largest Gravitational Lens: MACS J0717.5+3745 (z=0.546)

We identify 13 sets of multiply-lensed galaxies around MACS J0717.5+3745 ($z=0.546$), outlining a very large tangential critical curve of major axis $\sim2.8\arcmin$, filling the field of HST/ACS. The equivalent circular Einstein radius is $θ_{e}= 55 \pm 3\arcsec$ (at an estimated source redshift of $z_{s}\sim2.5$), corresponding to $r_e\simeq 350\pm 20 kpc$ at the cluster redshift, nearly three times greater than that of A1689 ($r_e\simeq 140 kpc$ for $z_{s}=2.5$). The mass enclosed by this critical curve is very large, $7.4\pm 0.5 \times 10^{14}M_{\odot}$ and only weakly model dependent, with a relatively shallow mass profile within $r<250 kpc$, reflecting the unrelaxed appearance of this cluster. This shallow profile generates a much higher level of magnification than the well known relaxed lensing clusters of higher concentration, so that the area of sky exceeding a magnification of $>10\times$, is $\simeq 3.5\sq\arcmin$ for sources with $z\simeq 8$, making MACS J0717.5+3745 a compelling target for accessing faint objects at high redshift. We calculate that only one such cluster, with $θ_{e}\ge 55\arcsec$, is predicted within $\sim 10^7$ Universes with $z\ge 0.55$, corresponding to a virial mass $\ge 3\times 10^{15} M_{\odot}$, for the standard $ΛCDM$ (WMAP5 parameters with $2σ$ uncertainties).

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arXiv2009

New Multiply-Lensed Galaxies Identified in ACS/NIC3 Observations of Cl0024+1654 Using an Improved Mass Model

We present an improved strong-lensing analysis of Cl0024+1654 ($z$=0.39) using deep HST/ACS/NIC3 images, based on 33 multiply-lensed images of 11 background galaxies. These are found with a model that assumes mass approximately traces light, with a low order expansion to allow for flexibility on large scales. The model is constrained initially by the well known 5-image system ($z$=1.675) and refined as new multiply-lensed systems are identified using the model. Photometric redshifts of these new systems are then used to constrain better the mass profile by adopting the standard cosmological relation between redshift and lensing distance. Our model requires only 6 free parameters to describe well all positional and redshift data. The resulting inner mass profile has a slope of $d\log M/d\log r\simeq -0.55$, consistent with new weak-lensing measurements where the data overlap, at $r\simeq200$ kpc/$h_{70}$. The combined profile is well fitted by a high concentration NFW mass profile, $C_{\rm vir}\sim 8.6\pm1.6$, similar to other well studied clusters, but larger than predicted with standard $Λ$CDM. A well defined radial critical curve is generated by the model and is clearly observed at $r \simeq 12\arcsec$, outlined by elongated images pointing towards the centre of mass. The relative fluxes of the multiply-lensed images are found to agree well with the modelled magnifications, providing an independent consistency check.

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arXiv2009

Discovery of the largest known lensed images formed by a critically convergent lensing cluster

We identify the largest known lensed images of a single spiral galaxy, lying close to the centre of the distant cluster MACS J1149.5+2223 ($z=0.544$). These images cover a total area of $\simeq 150 \Box\arcsec$ and are magnified $\simeq 200$ times. Unusually, there is very little image distortion implying the central mass distribution is almost uniform over a wide area ($r\simeq200 kpc$) with a surface density equal to the critical density for lensing, corresponding to maximal lens magnification. Many fainter multiply-lensed galaxies are also uncovered by our model, outlining a very large tangential critical curve, of radius $r\simeq 170 kpc$, posing a potential challenge for the standard LCDM-Cosmology. Because of the uniform central mass distribution a particularly clean measurement of the mass of the brightest cluster galaxy is possible here, for which we infer stars contribute most of the mass within a limiting radius of $\simeq 30 kpc$, with a mass-to-light ratio of $M/L_{B}\simeq 4.5(M/L)_{\odot}$. This cluster with its uniform and central mass distribution acts analogously to a regular magnifying glass, converging light without distorting the images, resulting in the most powerful lens yet discovered for accessing the faint high-$z$ Universe.

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arXiv2009

Star Formation Properties of Isolated Blue Compact Galaxies

We report H$α$ observations of a sample of very isolated blue compact galaxies (BCGs) located in the direction of large cosmic voids obtained to understand their stellar population compositions, the present star formation (SF) properties, and their star formation histories (SFHs). Our observations were combined with photometric data from the Sloan Digital Sky Survey (SDSS) and near-infrared data from the Two Micron All Sky Survey (2MASS), wherever such data were available. The combined data sets were compared with predictions of evolutionary synthesis models by Bruzual & Charlot (2003a, 2003b). Current star formation rates (SFRs) were determined from the H$α$ measurements, and simplified star formation histories were derived from broad-band and H$α$ photometry and comparisons with the models. We found that the star formation rates range within 0.1--1.0 M$_{\odot}$ yr$^{-1}$, with a median rate of 0.6 M$_{\odot}$ yr$^{-1}$. The observed galaxy colours are better explained by the combination of a continuous SF process with a recent instantaneous SF burst, than by a combination of several instantaneous bursts, as has been suggested previously. We compare our results for the star formation rate of the sample galaxies with that of samples of dwarf galaxies in the Virgo cluster and find that the BCGs have significantly stronger SFRs. The BCGs follow the correlation between H$α$ emission and starlight found for dwarf galaxies in the Virgo Cluster and for other BCGs.

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arXiv2009

Mass and Hot Baryons in Massive Galaxy Clusters from Subaru Weak Lensing and AMiBA SZE Observations

We present a multiwavelength analysis of a sample of four hot (T_X>8keV) X-ray galaxy clusters (A1689, A2261, A2142, and A2390) using joint AMiBA Sunyaev-Zel'dovich effect (SZE) and Subaru weak lensing observations, combined with published X-ray temperatures, to examine the distribution of mass and the intracluster medium (ICM) in massive cluster environments. Our observations show that A2261 is very similar to A1689 in terms of lensing properties. Many tangential arcs are visible around A2261, with an effective Einstein radius \sim 40 arcsec (at z \sim 1.5), which when combined with our weak lensing measurements implies a mass profile well fitted by an NFW model with a high concentration c_{vir} \sim 10, similar to A1689 and to other massive clusters. The cluster A2142 shows complex mass substructure, and displays a shallower profile (c_{vir} \sim 5), consistent with detailed X-ray observations which imply recent interaction. The AMiBA map of A2142 exhibits an SZE feature associated with mass substructure lying ahead of the sharp north-west edge of the X-ray core suggesting a pressure increase in the ICM. For A2390 we obtain highly elliptical mass and ICM distributions at all radii, consistent with other X-ray and strong lensing work. Our cluster gas fraction measurements, free from the hydrostatic equilibrium assumption, are overall in good agreement with published X-ray and SZE observations, with the sample-averaged gas fraction of = 0.133 \pm 0.027, for our sample = (1.2 \pm 0.1) \times 10^{15} M_{sun} h^{-1}. When compared to the cosmic baryon fraction f_b = Ω_b/Ω_m constrained by the WMAP 5-year data, this indicates /f_b = 0.78 \pm 0.16, i.e., (22 \pm 16)% of the baryons are missing from the hot phase of clusters.

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arXiv2008

The NGC 672 and NGC 784 Galaxy Groups: Evidence for Galaxy Formation and Growth Along a Nearby Dark Matter Filament

(Abridged): We present U, B, V, R, I, H-alpha and NUV photometry of 14 galaxies in the very local Universe (within 10 Mpc that are dwarf irregular galaxies (dIrr), are at low redshift (51 1-10 Gyr) and one "young" population (<30 Myr) with the recent SF bursts occurring a few to a few 10s of Myr ago, arguing for synchronicity in star formation in these objects. We propose that the ~synchronous star formation in all objects is caused by the accretion of cold gas from intergalactic space onto dark matter haloes arranged along a filament threading the void where these dwarf galaxies reside and point out this galaxy sample as an ideal target to study hierarchical clustering and galaxy formation among very nearby objects.

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