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Register a new userALMA observations of lensed Herschel sources : Testing the dark-matter halo paradigm
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Aristeidis Amvrosiads
Publication date
2018
fields
Physics
and research's language is
English
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With the advent of wide-area submillimeter surveys, a large number of high-redshift gravitationally lensed dusty star-forming galaxies (DSFGs) has been revealed. Due to the simplicity of the selection criteria for candidate lensed sources in such surveys, identified as those with $S_{500mu m} > 100$ mJy, uncertainties associated with the modelling of the selection function are expunged. The combination of these attributes makes submillimeter surveys ideal for the study of strong lens statistics. We carried out a pilot study of the lensing statistics of submillimetre-selected sources by making observations with the Atacama Large Millimetre Array (ALMA) of a sample of strongly-lensed sources selected from surveys carried out with the Herschel Space Observatory. We attempted to reproduce the distribution of image separations for the lensed sources using a halo mass function taken from a numerical simulation which contains both dark matter and baryons. We used three different density distributions, one based on analytical fits to the halos formed in the EAGLE simulation and two density distributions (Singular Isothermal Sphere (SIS) and SISSA) that have been used before in lensing studies. We found that we could reproduce the observed distribution with all three density distributions, as long as we imposed an upper mass transition of $sim$$10^{13} M_{odot}$ for the SIS and SISSA models, above which we assumed that the density distribution could be represented by an NFW profile. We show that we would need a sample of $sim$500 lensed sources to distinguish between the density distributions, which is practical given the predicted number of lensed sources in the Herschel surveys.
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The cusp-core problem is one of the main challenges of the cold dark matter paradigm on small scales: the density of a dark matter halo is predicted to rise rapidly toward the center as rho ~ r^alpha with alpha between -1 and -1.5, while such a cuspy profile has not been clearly observed. We have carried out the spatially-resolved mapping of gas dynamics toward a nearby ultra-diffuse galaxy (UDG), AGC 242019. The derived rotation curve of dark matter is well fitted by the cuspy profile as described by the Navarro-Frenk-White model, while the cored profiles including both the pseudo-isothermal and Burkert models are excluded. The halo has alpha=-(0.90+-0.08) at the innermost radius of 0.67 kpc, Mhalo=(3.5+-1.2)E10 Msun and a small concentration of 2.0+-0.36. AGC 242019 challenges alternatives of cold dark matter by constraining the particle mass of fuzzy dark matter to be < 0.11E-22 eV or > 3.3E-22 eV , the cross section of self-interacting dark matter to be < 1.63 cm2/g, and the particle mass of warm dark matter to be > 0.23 keV, all of which are in tension with other constraints. The modified Newtonian dynamics is also inconsistent with a shallow radial acceleration relationship of AGC 242019. For the feedback scenario that transforms a cusp to a core, AGC 242019 disagrees with the stellar-to-halo-mass-ratio dependent model, but agrees with the star-formation-threshold dependent model. As a UDG, AGC 242019 is in a dwarf-size halo with weak stellar feedback, late formation time, a normal baryonic spin and low star formation efficiency (SFR/gas).
The NGC 1052 group, and in particular the discovery of two ultra diffuse galaxies with very low internal velocity dispersions, has been the subject of much attention recently. Here we present radial velocities for a sample of 77 globular clusters associated with NGC 1052 obtained on the Keck telescope. Their mean velocity and velocity dispersion are consistent with that of the host galaxy. Using a simple tracer mass estimator, we infer the enclosed dynamical mass and dark matter fraction of NGC 1052. Extrapolating our measurements with an NFW mass profile we infer a total halo mass of 6.2 ($pm$0.2) $times$ 10$^{12}$ M$_{odot}$. This mass is fully consistent with that expected from the stellar mass--halo mass relation, suggesting that NGC 1052 has a normal dark matter halo mass (i.e. it is not deficient in dark matter in contrast to two ultra diffuse galaxies in the group). We present a phase space diagram showing the galaxies that lie within the projected virial radius (390 kpc) of NGC 1052. Finally, we briefly discuss the two dark matter deficient galaxies (NGC 1052--DF and DF4) and consider whether MOND can account for their low observed internal velocity dispersions.
We analyse systems analogous to the Milky Way (MW) in the EAGLE cosmological hydrodynamics simulation in order to deduce the likely structure of the MWs dark matter halo. We identify MW-mass haloes in the simulation whose satellite galaxies have similar kinematics and spatial distribution to those of the bright satellites of the MW, specifically systems in which the majority of the satellites (8 out of 11) have nearly co-planar orbits that are also perpendicular to the central stellar disc. We find that the normal to the common orbital plane of the co-planar satellites is well aligned with the minor axis of the host dark matter halo, with a median misalignment angle of only $17.3^circ$. Based on this result, we infer that the minor axis of the Galactic dark matter halo points towards $(l,b)=(182^circ,-2^circ)$, with an angular uncertainty at the 68 and 95 percentile confidence levels of 22$^circ$ and 43$^circ$ respectively. Thus, the inferred minor axis of the MW halo lies in the plane of the stellar disc. The halo, however, is not homologous and its flattening and orientation vary with radius. The inner parts of the halo are rounder than the outer parts and well-aligned with the stellar disc (that is the minor axis of the halo is perpendicular to the disc). Further out, the halo twists and the minor axis changes direction by $90^circ$. This twist occurs over a very narrow radial range and reflects variations in the filamentary network along which mass was accreted into the MW.
[Abridged] Aims: This work focuses on one lensed system, HATLAS J142935.3-002836 (H1429-0028), selected in the Herschel-ATLAS field. Gathering a rich, multi-wavelength dataset, we aim to confirm the lensing hypothesis and model the background sources morphology and dynamics, as well as to provide a full physical characterisation. Methods: Multi-wavelength high-resolution data is utilised to assess the nature of the system. A lensing-analysis algorithm which simultaneously fits different wavebands is adopted to characterise the lens. The background galaxy dynamical information is studied by reconstructing the 3-D source-plane of the ALMA CO(J:4-3) transition. Near-IR imaging from HST and Keck-AO allows to constrain rest-frame optical photometry independently for the foreground and background systems. Physical parameters (such as stellar and dust masses) are estimated via modelling of the spectral energy distribution taking into account source blending, foreground obscuration, and differential magnification. Results: The system comprises a foreground edge-on disk galaxy (at z_sp=0.218) with an almost complete Einstein ring around it. The background source (at z_sp=1.027) is magnified by a factor of ~8-10 depending on wavelength. It is comprised of two components and a tens of kpc long tidal tail resembling the Antennae merger. As a whole, the system is a massive stellar system (1.32[-0.41,+0.63] x1E11 Mo) forming stars at a rate of 394+-90 Mo/yr, and has a significant gas reservoir M_ISM = 4.6+-1.7 x1E10 Mo. Its depletion time due to star formation alone is thus expected to be tau_SF=M_ISM/SFR=117+-51 Myr. The dynamical mass of one of the components is estimated to be 5.8+-1.7 x1E10 Mo, and, together with the photometric total mass estimate, it implies that H1429-0028 is a major merger system (1:2.8[-1.5,+1.8]).
We have modelled high resolution ALMA imaging of six strong gravitationally lensed galaxies detected by the Herschel Space Observatory. Our modelling recovers mass properties of the lensing galaxies and, by determining magnification factors, intrinsic properties of the lensed sub-millimetre sources. We find that the lensed galaxies all have high ratios of star formation rate to dust mass, consistent with or higher than the mean ratio for high redshift sub-millimetre galaxies and low redshift ultra-luminous infra-red galaxies. Source reconstruction reveals that most galaxies exhibit disturbed morphologies. Both the cleaned image plane data and the directly observed interferometric visibilities have been modelled, enabling comparison of both approaches. In the majority of cases, the recovered lens models are consistent between methods, all six having mass density profiles that are close to isothermal. However, one system with poor signal to noise shows mildly significant differences.
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