arXiv subjects

Tom Broadhurst

Publications and source records attributed to Tom Broadhurst.

At least 73 records · Page 4Linked to original sources

arXiv2020

Sustained formation of progenitor globular clusters in a giant elliptical galaxy

Globular clusters (GCs) are thought to be ancient relics from the early formative phase of galaxies, although their physical origin remains uncertain. GCs are most numerous around massive elliptical galaxies, where they can exhibit a broad colour dispersion, suggesting a wide metallicity spread. Here, we show that many thousands of compact and massive (~5$\times$10$^{\rm 3}-$3$\times$ 10$^{\rm 6} M_{\odot}$) star clusters have formed at an approximately steady rate over, at least, the past ~1Gyr around NGC 1275, the central giant elliptical galaxy of the Perseus cluster. Beyond ~1Gyr, these star clusters are indistinguishable in broadband optical colours from the more numerous GCs. Their number distribution exhibits a similar dependence with luminosity and mass as the GCs, whereas their spatial distribution resembles a filamentary network of multiphase gas associated with cooling of the intracluster gas. The sustained formation of these star clusters demonstrates that progenitor GCs can form over cosmic history from cooled intracluster gas, thus contributing to both the large number and broad colour dispersion$-$owing to an age spread, in addition to a spread in metallicity$-$of GCs in massive elliptical galaxies. The progenitor GCs have minimal masses well below the maximal masses of Galactic open star clusters, affirming a common formation mechanism for star clusters over all mass scales irrespective of their formative pathways.

astro-ph.GA↗

arXiv2020

Multiple Images and Flux Ratio Anomaly of Fuzzy Gravitational Lenses

Extremely light bosonic wave dark matter ($ψ$DM) is an emerging dark matter candidate contesting the conventional cold dark matter paradigm and a model subject to intense scrutiny of late. This work for the first time reports testable salient features pertinent to gravitational lenses of $ψ$DM halos. $ψ$DM halos are distinctly filled with large-amplitude, small-scale density fluctuations with $δρ/ρ_{\rm halo}\sim 1$ in form of density granules. This halo yields ubiquitous flux ratio anomalies of a few tens of percent, as is typically found for lensed quasars, and may also produce rare hexad and octad images, for sources located in well-defined caustic zones. We have found new critical features appearing in the highly de-magnified lens center when the halo has sufficiently high surface density near a very compact massive core.

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arXiv2020

A Strong-Lensing Model for the WMDF JWST/GTO Very Rich Cluster Abell 1489

We present a first strong-lensing model for the galaxy cluster RM J121218.5+273255.1 ($z=0.35$; hereafter RMJ1212; also known as Abell 1489). This cluster is amongst the top 0.1\% richest clusters in the redMaPPer catalog; it is significantly detected in X-ray and through the Sunyaev-Zel'dovich effect in ROSAT and \emph{Planck} data, respectively; and its optical luminosity distribution implies a very large lens, following mass-to-light scaling relations. Based on these properties it was chosen for the Webb Medium Deep Fields (WMDF) JWST/GTO program. In preparation for this program, RMJ1212 was recently imaged with GMOS on Gemini North and in seven optical and near-infrared bands with the \emph{Hubble Space Telescope}. We use these data to map the inner mass distribution of the cluster, uncovering various sets of multiple images. We also search for high-redshift candidates in the data, as well as for transient sources. We find over a dozen high-redshift ($z\gtrsim6$) candidates based on both photometric redshift and the dropout technique. No prominent ($\gtrsim5 σ$) transients were found in the data between the two HST visits. Our lensing analysis reveals a relatively large lens with an effective Einstein radius of $θ_{E}\simeq32\pm3''$ ($z_{s}=2$), in broad agreement with the scaling-relation expectations. RMJ1212 demonstrates that powerful lensing clusters can be selected in a robust and automated way following the light-traces-mass assumption.

astro-ph.GA↗

arXiv2020

Geometric Support for Dark Matter by an Unaligned Einstein Ring in Abell 3827

The non-detection of dark matter (DM) particles in increasingly stringent laboratory searches has encouraged alternative gravity theories where gravity is sourced only from visible matter. Here, we consider whether such theories can pass a two-dimensional test posed by gravitational lensing -- to reproduce a particularly detailed Einstein ring in the core of the galaxy cluster Abell 3827. We find that when we require the lensing mass distribution to strictly follow the shape (ellipticity and position angle) of the light distribution of cluster member galaxies, intracluster stars, and the X-ray emitting intracluster medium, we cannot reproduce the Einstein ring, despite allowing the mass-to-light ratios of these visible components to freely vary with radius to mimic alternative gravity theories. Alternatively, we show that the detailed features of the Einstein ring are accurately reproduced by allowing a smooth, freely oriented DM halo in the lens model, with relatively small contributions from the visible components at a level consistent with their observed brightnesses. This dominant DM component is constrained to have the same orientation as the light from the intracluster stars, indicating that the intracluster stars trace the gravitational potential of this component. The Einstein ring of Abell 3827 therefore presents a new challenge for alternative gravity theories: not only must such theories find agreement between the total lensing mass and visible mass, but they must also find agreement between the projected sky distribution of the lensing mass and that of the visible matter, a more stringent test than has hitherto been posed by lensing data.

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arXiv2020

Interpreting LIGO/Virgo "Mass-Gap" events as lensed Neutron Star-Black Hole binaries

Gravitational lensing allows the detection of binary black holes (BBH) at cosmological distances with chirp masses that appear to be enhanced by $1+z$ in the range $1 95\%$), from which we infer a factor $\simeq 5$ higher intrinsic rate of NSBH events than BBH events, reflecting a higher proportion of neutron stars formed by early star formation. We predict a distinctive locus for lensed NSBH events in the observed binary mass plane, spanning $1<z<4$ with a narrow mass ratio, $q \simeq 0.2$, that can be readily tested when the waveform data are unlocked. All such events may show disrupted NS emission and are worthy of prompt follow-up as the high lensing magnification means EM detections are not prohibitive despite the high redshifts that we predict. Such lensed NSBH events provide an exciting prospect of directly charting the history of coalescing binaries via the cosmological redshift of their waveforms, determined relative to the characteristic mass of the neutron star member.

astro-ph.CO↗

arXiv2020

Multiple Ultralight Axionic Wave Dark Matter and Astronomical Structures

An ultralight scalar boson with mass $m_1 \simeq 10^{-22}$ eV is gaining credence as a Dark Matter (DM) candidate that explains the dark cores of dwarf galaxies as soliton waves. Such a boson is naturally interpreted as an axion generic in String Theory, with multiple light axions predicted in this context. We examine the possibility of soliton structures over a wide range of scales, accounting for galaxy core masses and the common presence of nuclear star clusters. We present a diagnostic soliton core mass-radius plot that provides a global view, indicating the existence of an additional axion with mass $m_2\simeq 10^{-20}$ eV, with the possibility of a third axion with mass $m_3 \gtrsim 0.5 \times 10^{-18}$ eV. We also argue that the relative mass densities measured for these axions are consistent with their cosmological production via the mis-alignment mechanism.

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arXiv2020

Soliton Random Walk and the Cluster-Stripping Problem in Ultralight Dark Matter

Simulations of ultralight, $\sim 10^{-22}\,\rm eV$, bosonic dark matter exhibit rich wave-like structure, including a soliton core within a surrounding halo that continuously self-interferes on the de Broglie scale. We show here that as an inherent consequence, the soliton undergoes a confined random walk at the base of the halo potential. This is significant for the fate of the ancient central star cluster in Eridanus II, as the agitated soliton gravitationally shakes the star cluster in and out of the soliton on a time scale of $\sim 100\,\rm Myr$, so complete tidal disruption of the star cluster can occur within $\sim 1\,\rm Gyr$. This destructive effect can be mitigated by tidal stripping of the halo of Eridanus II, thereby reducing the agitation, depending on its orbit around the Milky Way. Our simulations show the Milky Way tide affects the halo much more than the soliton, so the star cluster in Eridanus II can survive for over $5\,\rm Gyr$ within the soliton if it formed after significant halo stripping.

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arXiv2020

Ghostly Galaxies as Solitons of Bose-Einstein Dark Matter

The large dark cores of common dwarf galaxies are unexplained by the standard heavy particle interpretation of dark matter. This puzzle is exacerbated by the discovery of a very large but barely visible, dark matter dominated galaxy Antlia II orbiting the Milky Way, uncovered by tracking star motions with the {\t Gaia} satellite. Although Antlia II has a low mass, its visible radius is more than double any known dwarf galaxy, with an unprecedentedly low density core. We show that Antlia II favors dark matter as a Bose-Einstein condensate, for which the ground state is a stable soliton with a core radius given by the de Broglie wavelength. The lower the galaxy mass, the larger the de Broglie wavelength, so the least massive galaxies should have the widest soliton cores of lowest density. An ultra-light boson of $m_ψ\sim 1.1 \times10^{-22}$ eV, accounts well for the large size and slowly moving stars within Antlia II, and agrees with boson mass estimates derived from the denser cores of more massive dwarf galaxies. For this very light boson, Antlia II is close to the lower limiting Jeans scale for galaxy formation permitted by the Uncertainty Principle, so other examples are expected but none significantly larger in size. This simple explanation for the puzzling dark cores of dwarf galaxies implies dark matter as an ultra-light boson, such as an axion generic in String Theory.

astro-ph.CO↗

arXiv2020

A Soliton Solution for the Central Dark Masses in 47- Tuc Globular Cluster and Implications for the Axiverse

We offer a standing wave explanation for the rising proper motions of stars at the center of the globular cluster 47-Tucanae, amounting to $\simeq 0.44\%$ of the total mass. We show this can be explained as a solitonic core of dark matter composed of light bosons, $ m \geq 10^{-18} eV $, corresponding to $ \leq 0.27 pc$, as an alternative to a single black hole (BH) or a concentration of stellar BH remnants proposed recently. This is particularly important as having a concentrated stellar BH remnant with the above radii is very challenging without the heavy core since the three body encounters would prevent the BHs to be that concentrated. We propose this core develops from dark matter captured in the deep gravitational potential of this globular cluster as it orbits the dark halo of our galaxy. This boson may be evidence for a second light axion, additional to a lighter boson of $10^{-22} eV$, favored for the dominant dark matter implied by the large dark cores of dwarf spheroidal galaxies. The identification of two such light bosonic mass scales favors the generic string theory prediction of a wide, discrete mass spectrum of axionic scalar fields.

astro-ph.CO↗

arXiv2020

The BUFFALO HST Survey

The Beyond Ultra-deep Frontier Fields and Legacy Observations (BUFFALO) is a 101 orbit + 101 parallel Cycle 25 Hubble Space Telescope Treasury program taking data from 2018-2020. BUFFALO will expand existing coverage of the Hubble Frontier Fields (HFF) in WFC3/IR F105W, F125W, and F160W and ACS/WFC F606W and F814W around each of the six HFF clusters and flanking fields. This additional area has not been observed by HST but is already covered by deep multi-wavelength datasets, including Spitzer and Chandra. As with the original HFF program, BUFFALO is designed to take advantage of gravitational lensing from massive clusters to simultaneously find high-redshift galaxies which would otherwise lie below HST detection limits and model foreground clusters to study properties of dark matter and galaxy assembly. The expanded area will provide a first opportunity to study both cosmic variance at high redshift and galaxy assembly in the outskirts of the large HFF clusters. Five additional orbits are reserved for transient followup. BUFFALO data including mosaics, value-added catalogs and cluster mass distribution models will be released via MAST on a regular basis, as the observations and analysis are completed for the six individual clusters.

astro-ph.GA↗

arXiv2020

Dynamical Evidence of a Solitonic Core of $10^{9}M_\odot$ in the Milky Way

A wavelike solution for the non-relativistic universal dark matter (wave-DM) is rapidly gaining interest, following distinctive predictions of pioneering simulations of cosmic structure as an interference pattern of coherently oscillating bosons. A prominent solitonic standing wave is predicted at the center of every galaxy, representing the ground state, that has been identified with the wide, kpc scale dark cores of common dwarf-spheroidal galaxies, providing a boson mass of, $\simeq 10^{-22}$ eV. A denser soliton is predicted for Milky Way sized galaxies where momentum is higher, so the de Broglie scale of the soliton is smaller, $\simeq 100$ pc, of mass $\simeq 10^9 M_\odot$. Here we show the central motion of bulge stars in the Milky Way implies the presence of such a dark core, where the velocity dispersion rises inversely with radius to a maximum of $\simeq 130$ km/s, corresponding to an excess central mass of $\simeq 1.5\times 10^9 M_\odot$ within $\simeq 100$ pc, favouring a boson mass of $\simeq 10^{-22}$ eV. This quantitative agreement with such a unique and distinctive prediction is therefore strong evidence for a light bosonic solution to the long standing Dark Matter puzzle, such as the axions generic in String Theory.

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arXiv2019

Evidence of Neutrino Enhanced Clustering in a Complete Sample of Sloan Survey Clusters, Implying $\sum m_ν= 0.119 \pm 0.034$ eV

The clustering amplitude of 7143 clusters from the Sloan Digital Sky Survey (SDSS) is found to increase with cluster mass, closely agreeing with the Gaussian random field hypothesis for structure formation. The amplitude of the observed cluster correlation exceeds the predictions from pure cold dark matter (CDM) simulation by $\simeq 6\%$ for the standard Planck-based values of the cosmological parameters. We show that this excess can be naturally accounted for by free streaming of light neutrinos, which opposes gravitational growth, so clusters formed at fixed mass are fewer and hence more biased than for a pure CDM density field. An enhancement of the cluster bias by 7\% matches the observations, corresponding to a total neutrino mass, $m_ν = 0.119 \pm 0.034$ eV at 67\% confidence level, for the standard relic neutrino density. If ongoing laboratory experiments favor a normal neutrino mass hierarchy then we may infer a somewhat larger total mass than the minimum oscillation based value, $\sum m_ν \simeq 0.056eV$, with 90\% confidence. Much higher precision can be achieved by applying our method to a larger sample of more distant clusters with weak lensing derived masses.

astro-ph.CO↗

arXiv2019

Detection of a Lensed z$\approx$11 Galaxy in the Rest-Optical with Spitzer/IRAC and the Inferred SFR, Stellar Mass, and Physical Size

We take advantage of new 100-hour Spitzer/IRAC observations available for MACS0647-JD, a strongly lensed $z\approx11$ galaxy candidate, to provide improved constraints on its physical properties. Probing the physical properties of galaxies at $z>8$ is challenging due to the inherent faintness of such sources and the limited wavelength coverage available. Thanks to the high $\approx$2-6$\times$ lensing magnification of the multiple images of MACS0647-JD, we can use the sensitive Spitzer/IRAC data to probe the rest-frame optical fluxes of MACS0647-JD and investigate its physical properties including the age and the stellar mass. In deriving Spitzer/IRAC fluxes for MACS0647-JD, great care is taken in coping with the impact of three bright ($\approx$8-16 mag) stars in our field to ensure robust results. Assuming a constant star formation rate, the age, stellar mass, and rest-frame UV slope we estimate for MACS0647-JD based on a stack of the photometry are log$_{10}$(age/yr) = 8.6$^{+0.1}_{-2.1}$, log$_{10}$(M$_{*}$/M$_{\odot}$) = 9.1$^{+0.2}_{-1.4}$, and $β= -$1.3$\pm$0.6, respectively. We compare our results with expectations from the EAGLE simulation and find that MACS0647-JD has properties consistent with corresponding to the most massive and rapidly star-forming galaxies in the simulation. We also find that its radius, 105$\pm$28 pc, is a factor of $\approx$2 smaller than the mean size in a separate simulation project DRAGONS. Interestingly enough, the observed size is similar to the small sizes seen in very low-luminosity $z\approx$6-10 galaxies behind lensing clusters.

astro-ph.GA↗

arXiv2019

Twin LIGO/Virgo Detections of a Viable Gravitationally-Lensed Black Hole Merger

We identify a binary black hole (BBH) merger that appears to be multiply lensed by an intervening galaxy. The LIGO/Virgo events GW170809 and GW170814 have indistinguishable waveforms separated by 5 days, and overlap on the sky within the 90\% credible region. Their strain amplitudes are also similar, implying a modest relative magnification ratio, as expected for a pair of lensed gravitational waves. The phase of the two events is also consistent with being the same, adding more evidence in support of both events originating from the same BBH merger. The difference in the published inferred distances of each event can then be interpreted as following from their different magnifications. The observed chirp masses of both events are also similar, as expected for a pair of lensed events, with a common detected value of $29.1^{+1.3}_{-1.0}M_{\odot}$, lying at the peak of the observed distribution of chirp masses. We infer this case is a prototypical example of a lensed event that supports our lensing prediction \cite{Broadhurst2018} according to which, cosmologically distant, magnified BBH comprise most of the LIGO/Virgo events with chirp masses enhanced above $\simeq 15M_{\odot}$ by the cosmological expansion. From our predictions we estimate an intrinsic, unlensed, chirp mass of $\simeq 10-12 M_\odot$, with a source redshift in the range $0.9<z<2.5$. We also outline a joint analysis over all baseline permutations that can stringently test our lensing interpretation of these two events. More generally, lensed events effectively multiply the number of baseline permutations and motivates the use of more interferometers for round the clock coverage of all repeat events of a given source, in order to maximise the orbital details and sky localization of lensed BBH sources.

astro-ph.CO↗

arXiv2018

Discovering intermediate-mass black hole lenses through gravitational wave lensing

Intermediate-mass black holes are the missing link that connects stellar-mass to supermassive black holes and are key to understanding galaxy evolution. Gravitational waves, like photons, can be lensed, leading to discernable effects such as diffraction or repeated signals. We investigate the detectability of intermediate-mass black hole deflectors in the LIGO-Virgo detector network. In particular, we simulate gravitational waves with variable source distributions lensed by an astrophysical population of intermediate-mass black holes, and use standard LIGO tools to infer the properties of these lenses. We find detections of intermediate-mass black holes at $98\%$ confidence level over a wide range of binary and lens parameters. Therefore, we conclude that intermediate-mass black holes could be detected through lensing of gravitational waves in the LIGO-Virgo detector network.

gr-qc↗

arXiv2018

A Likely Super Massive Black Hole Revealed by its Einstein Radius in Hubble Frontier Fields Images

At cosmological distances, gravitational lensing can provide a direct measurement of supermassive black hole (SMBH) masses irrespective of their luminosities. Here, we directly estimate the mass of a SMBH in the brightest cluster galaxy (BCG) of MACS J1149+2223.5 at $z=0.54$ through one of the multiply-lensed images of a background spiral galaxy at $z=1.49$ projected close to the BCG. In this particular image, an intrinsically compact region in one of the spiral arms is lensed into an arc that curves towards the BCG center. This arc has a radius of curvature of only $\sim$0."6, betraying the presence of a local compact deflector. Its curvature is most simply reproduced by a point-like object with a mass of $8.4^{+4.3}_{-1.8}\times10^{9}M_\odot$, similar to SMBH masses in local elliptical galaxies having comparable luminosities. The SMBH is noticeably offset by $4.4\pm0.3$ kpc from the BCG light centre, plausibly the result of a kick imparted $\sim2.0\times10^7$ years ago during the merger of two SMBHs, placing it just beyond the stellar core. A similar curvature can be produced by replacing the offset SMBH with a compact galaxy having a mass of $\sim2\times 10^{10}M_\odot$ within a cutoff radius of $<4$ kpc, and an unusually large $M/L>50(M/L)_\odot$ to make it undetectable in the deep Hubble Frontiers Fields image, at or close to the cluster redshift; such a lensing galaxy, however, perturbs the adjacent lensed images in an undesirable way.

astro-ph.GA↗

arXiv2018

Magnification Bias of Distant Galaxies in the Hubble Frontier Fields: Testing Wave vs. Particle Dark Matter Predictions

Acting as powerful gravitational lenses, the strong lensing galaxy clusters of the deep Hubble Frontier Fields (HFF) program permit access to lower-luminosity galaxies lying at higher redshifts than hitherto possible. We analyzed the HFF to measure the volume density of Lyman-break galaxies at $z > 4.75$ by identifying a complete and reliable sample up to $z \simeq 10$. A marked deficit of such galaxies was uncovered in the highly magnified regions of the clusters relative to their outskirts, implying that the magnification of the sky area dominates over additional faint galaxies magnified above the flux limit. This negative magnification bias is consistent with a slow rollover at the faint end of the UV luminosity function, and indicates a preference for Bose-Einstein condensate dark matter with a light boson mass of $m_\mathrm{B} \simeq 10^{-22} \, \mathrm{eV}$ over standard cold dark matter. We emphasize that measuring the magnification bias requires no correction for multiply lensed images (with typically three or more images per source), whereas directly reconstructing the luminosity function will lead to an overestimate unless such images can be exhaustively matched up, especially at the faint end that is accessible only in the strongly lensed regions. In addition, we detected a distinctive downward transition in galaxy number density at $z \gtrsim 8$, which may be linked to the relatively late reionization reported by Planck. Our results suggests that JWST will likely peer into an "abyss" with essentially no galaxies detected in deep NIR imaging at $z > 10$.

astro-ph.GA↗

arXiv2018

The Projected Dark and Baryonic Ellipsoidal Structure of 20 CLASH Galaxy Clusters

We reconstruct the two-dimensional (2D) matter distributions in 20 high-mass galaxy clusters selected from the CLASH survey by using the new approach of performing a joint weak lensing analysis of 2D shear and azimuthally averaged magnification measurements. This combination allows for a complete analysis of the field, effectively breaking the mass-sheet degeneracy. In a Bayesian framework, we simultaneously constrain the mass profile and morphology of each individual cluster assuming an elliptical Navarro-Frenk-White halo characterized by the mass, concentration, projected axis ratio, and position angle of the projected major axis.. We find that spherical mass estimates of the clusters from azimuthally averaged weak-lensing measurements in previous work are in excellent agreement with our results from a full 2D analysis. Combining all 20 clusters in our sample, we detect the elliptical shape of weak-lensing halos at the $5σ$ significance level within a scale of 2Mpc$/h$. The median projected axis ratio is $0.67\pm 0.07$ at a virial mass of $M_\mathrm{vir}=(15.2\pm 2.8) \times 10^{14} M_\odot$, which is in agreement with theoretical predictions of the standard collisionless cold dark matter model. We also study misalignment statistics of the brightest cluster galaxy, X-ray, thermal Sunyaev-Zel'dovich effect, and strong-lensing morphologies with respect to the weak-lensing signal. Among the three baryonic tracers studied here, we find that the X-ray morphology is best aligned with the weak-lensing mass distribution, with a median misalignment angle of $21\pm 7$ degrees. We also conduct a stacked quadrupole shear analysis assuming that the X-ray major axis is aligned with that of the projected mass distribution. This yields a consistent axis ratio of $0.67\pm 0.10$, suggesting again a tight alignment between the intracluster gas and dark matter.

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