arXiv subjects

Alister W. Graham

Publications and source records attributed to Alister W. Graham.

At least 55 records · Page 3Linked to original sources

arXiv2021

Refining the mass estimate for the intermediate-mass black hole candidate in NGC 3319

Recent X-ray observations by Jiang et al. have identified an active galactic nucleus (AGN) in the bulgeless spiral galaxy NGC 3319, located just $14.3\pm1.1\,$Mpc away, and suggest the presence of an intermediate-mass black hole (IMBH; $10^2\leq M_\bullet/\mathrm{M_{\odot}}\leq10^5$) if the Eddington ratios are as high as 3 to $3\times10^{-3}$. In an effort to refine the black hole mass for this (currently) rare class of object, we have explored multiple black hole mass scaling relations, such as those involving the (not previously used) velocity dispersion, logarithmic spiral-arm pitch angle, total galaxy stellar mass, nuclear star cluster mass, rotational velocity, and colour of NGC 3319, to obtain ten mass estimates, of differing accuracy. We have calculated a mass of $3.14_{-2.20}^{+7.02}\times10^4\,\mathrm{M_\odot}$, with a confidence of 84% that it is $\leq$$10^5\,\mathrm{M_\odot}$, based on the combined probability density function from seven of these individual estimates. Our conservative approach excluded two black hole mass estimates (via the nuclear star cluster mass, and the fundamental plane of black hole activity $\unicode{x2014}$ which only applies to black holes with low accretion rates) that were upper limits of $\sim$$10^5\,{\rm M}_{\odot}$, and it did not use the $M_\bullet\unicode{x2013}L_{\rm 2-10\,keV}$ relation's prediction of $\sim$$10^5\,{\rm M}_{\odot}$. This target provides an exceptional opportunity to study an IMBH in AGN mode and advance our demographic knowledge of black holes. Furthermore, we introduce our novel method of meta-analysis as a beneficial technique for identifying new IMBH candidates by quantifying the probability that a galaxy possesses an IMBH.

astro-ph.GA↗

arXiv2021

History of Astronomy in Australia: Big-Impact Astronomy from World War II until the Lunar Landing (1945-1969)

Radio astronomy commenced in earnest after World War II, with Australia keenly engaged through the Council for Scientific and Industrial Research. At this juncture, Australia's Commonwealth Solar Observatory expanded its portfolio from primarily studying solar phenomena to conducting stellar and extragalactic research. Subsequently, in the 1950s and 1960s, astronomy gradually became taught and researched in Australian universities. However, most scientific publications from this era of growth and discovery have no country of affiliation in their header information, making it hard to find the Australian astronomy articles from this period. In 2014, we used the then-new Astrophysics Data System (ADS) tool Bumblebee to overcome this challenge and track down the Australian-led astronomy papers published during the quarter of a century after World War II, from 1945 until the lunar landing in 1969. This required knowledge of the research centres and facilities operating at the time, which are briefly summarised herein. Based on citation counts -- an objective, universally-used measure of scientific impact -- we report on the Australian astronomy articles which had the biggest impact. We have identified the top-ten most-cited papers, and thus also their area of research, from five consecutive time-intervals across that blossoming quarter-century of astronomy. Moreover, we have invested a substantial amount of time researching and providing a small tribute to each of the 62 scientists involved, including several trail-blazing women. Furthermore, we provide an extensive list of references and point out many interesting historical connections and anecdotes.

physics.hist-ph↗

arXiv2021

Defining the (Black Hole)-Spheroid Connection with the Discovery of Morphology-Dependent Substructure in the $M_{\rm BH}$--$\rm n_{sph}$ and $M_{\rm BH}$--$\rm R_{e, sph}$ Diagrams: New Tests for Advanced Theories and Realistic Simulations

For 123 local galaxies with directly-measured black hole masses ($M_{\rm BH}$), we provide the host spheroid's Sérsic index ($\rm n_{sph}$), effective half-light radius ($\rm R_{e,sph}$), and effective surface brightness ($μ_e$), obtained from careful multi-component decompositions, and we use these to derive the morphology-dependent $M_{\rm BH}$--$\rm n_{sph}$ and $M_{\rm BH}$--$\rm R_{e,sph}$ relations. We additionally present the morphology-dependent $M_{\rm *,sph}$--$\rm n_{sph}$ and $M_{\rm *,sph}$--$\rm R_{e,sph}$ relations. We explored differences due to: early-type galaxies (ETGs) versus late-type galaxies (LTGs); Sérsic versus core-Sérsic galaxies; barred versus non-barred galaxies; and galaxies with and without a stellar disk. We detect two different $M_{\rm BH}$--$\rm n_{sph}$ relations due to ETGs and LTGs with power-law slopes $3.95\pm0.34$ and $2.85\pm 0.31$. We additionally quantified the correlation between $M_{\rm BH}$ and the spheroid's central concentration index, which varies monotonically with the Sérsic index. Furthermore, we observe a single, near-linear $M_{\rm *,sph}$--$\rm R_{e,sph}^{1.08\pm 0.04}$ relation for ETGs and LTGs, which encompasses both classical and alleged pseudobulges. In contrast, ETGs and LTGs define two distinct $M_{\rm BH}$--$\rm R_{e,sph}$ relations with $Δ_{\rm rms|BH}\sim\rm 0.60~dex$ (cf.\ $\sim$0.51~dex for the $M_{\rm BH}$--$σ$ relation and $\sim$0.58~dex for the $M_{\rm BH}$--$M_{\rm *,sph}$ relation), and the ETGs alone define two steeper $M_{\rm BH}$--$\rm R_{e,sph}$ relations, offset by $\sim$1~dex in the $\log M_{\rm BH}$-direction, depending on whether they have a disk or not and explaining their similar offset in the $M_{\rm BH}$--$M_{\rm *,sph}$ diagram. This trend holds using $10 \%$, $50 \%$, or $90 \%$ radii.(Abridged)

astro-ph.GA↗

arXiv2020

KiDS+GAMA: The weak lensing calibrated stellar-to-halo mass relation of central and satellite galaxies

We simultaneously present constraints on the stellar-to-halo mass relation for central and satellite galaxies through a weak lensing analysis of spectroscopically classified galaxies. Using overlapping data from the fourth data release of the Kilo-Degree Survey (KiDS), and the Galaxy And Mass Assembly survey (GAMA), we find that satellite galaxies are hosted by halo masses that are $0.53 \pm 0.39$ dex (68\% confidence, $3σ$ detection) smaller than those of central galaxies of the same stellar mass (for a stellar mass of $\log(M_{\star}/M_{\odot}) = 10.6$). This is consistent with galaxy formation models, whereby infalling satellite galaxies are preferentially stripped of their dark matter. We find consistent results with similar uncertainties when comparing constraints from a standard azimuthally averaged galaxy-galaxy lensing analysis and a two-dimensional likelihood analysis of the full shear field. As the latter approach is somewhat biased due to the lens incompleteness and as it does not provide any improvement to the precision when applied to actual data, we conclude that stacked tangential shear measurements are best-suited for studies of the galaxy-halo connection.

astro-ph.CO↗

arXiv2019

A consistency-test for determining whether ultra-compact dwarf galaxies could be the remnant nuclei of threshed galaxies

It has been suggested that ultra-compact dwarf (UCD) galaxies are the "threshed'" remains of larger galaxies. Simulations have revealed that extensive tidal-stripping may pare a galaxy back to its tightly-bound, compact nuclear star cluster. It has therefore been proposed that the two-component nature of UCD galaxies may reflect the original nuclear star cluster surrounded by the paltry remnants of its host galaxy. A simple quantitative test of this theory is devised and applied here. If the mass of the central black hole in UCD galaxies, relative to the mass of the UCD galaxies' inner stellar component, i.e. the suspected nuclear star cluster, matches with the (black hole mass)-(nuclear star cluster mass) relation observed in other galaxies, then it would provide quantitative support for the stripped galaxy scenario. Such consistency is found for four of the five UCD galaxies reported to have a massive black hole. The (black hole mass)-(nuclear star cluster mass) relation is then used to predict the central black hole mass in two additional UCD galaxies, and to reveal that NGC 205 and possibly NGC 404 (which only has an upper limit to its black hole mass) also follow this scaling relation.

astro-ph.GA↗

arXiv2019

Revealing Hidden Substructures in the $M_{BH}$-$σ$ Diagram, and Refining the Bend in the $L$-$σ$ Relation

Using 145 early- and late-type galaxies (ETGs and LTGs) with directly-measured super-massive black hole masses, $M_{BH}$, we build upon our previous discoveries that: (i) LTGs, most of which have been alleged to contain a pseudobulge, follow the relation $M_{BH}\propto\,M_{*,sph}^{2.16\pm0.32}$; and (ii) the ETG relation $M_{BH}\propto\,M_{*,sph}^{1.27\pm0.07}$ is an artifact of ETGs with/without disks following parallel $M_{BH}\propto\,M_{*,sph}^{1.9\pm0.2}$ relations which are offset by an order of magnitude in the $M_{BH}$-direction. Here, we searched for substructure in the $M_{BH}$--(central velocity dispersion, $σ$) diagram using our recently published, multi-component, galaxy decompositions; investigating divisions based on the presence of a depleted stellar core (major dry-merger), a disk (minor wet/dry-merger, gas accretion), or a bar (evolved unstable disk). The Sérsic and core-Sérsic galaxies define two distinct relations: $M_{BH}\proptoσ^{5.75\pm0.34}$ and $M_{BH}\proptoσ^{8.64\pm1.10}$, with $Δ_{rms|BH}=0.55$ and $0.46$~dex, respectively. We also report on the consistency with the slopes and bends in the galaxy luminosity ($L$)--$σ$ relation due to Sérsic and core-Sérsic ETGs, and LTGs which all have Sérsic light-profiles. Two distinct relations (superficially) reappear in the $M_{BH}$--$σ$ diagram upon separating galaxies with/without a disk (primarily for the ETG sample), while we find no significant offset between barred and non-barred galaxies, nor between galaxies with/without active galactic nuclei. We also address selection biases purported to affect the scaling relations for dynamically-measured $M_{BH}$ samples. Our new, (morphological type)-dependent, $M_{BH}$--$σ$ relations more precisely estimate $M_{BH}$ in other galaxies, and hold implications for galaxy/black hole co-evolution theories, and simulations. (Abridged)

astro-ph.GA↗

arXiv2019

$R_{\rm e}$. I. Understanding galaxy sizes, associated luminosity densities, and the artificial division of the early-type galaxy population

The deceptive simplicity of the radius enclosing an arbitrary 50 percent of a galaxy's light has hamstrung the understanding of early-type galaxies (ETGs). Half a century ago, using the "effective half-light radii" $R_e$ from de Vaucouleurs' $R^{1/4}$ model, Sérsic reported that bright ETGs follow the relation $\mathfrak{M}_B\propto2.5\log R_e$; and consequently one has that $\langleμ\rangle_e\propto2.5\log R_e$ and $μ_e\propto2.5\log R_e$, where $μ_e$ and $\langleμ\rangle_e$ are the effective surface brightness at $R_e$ and the mean effective surface brightness within $R_e$, respectively. Sérsic additionally observed an apparent transition which led him to advocate for a division between what he called dwarf and giant ETGs; a belief frequently restated to occur at $\mathfrak{M}_B\approx-18$ mag or Sérsic $n\approx 2.5$. Here, the location of this false dichotomy is shown to change by more than 3 mag simply depending on the arbitrary percentage of light used to quantify a galaxy's size, voiding claims for different formation physics operating on ETGs brighter and fainter than $\mathfrak{M}_B\approx-18$ mag. This is of further importance because quantities such as dynamical mass $σ^2R/G$, gravitational binding energy $GM^2/R$, acceleration $GM/R^2$, and the "Fundamental Plane" depend systematically on the arbitrary percentage of light used to define $R$, with implications for dark matter estimates, galaxy formation theories, compact massive galaxies, studies of peculiar velocity flows, and more. Finally, some of the vast literature which has advocated for segregating the ETG population at $\mathfrak{M}_B\approx-18$ mag ($M\approx1$-$2\times10^{10}\,M_{\odot}$) is addressed, and it is revealed how this pervasive mindset has spilled-over to influence both the classical bulge versus pseudobulge debate and recently also correlations involving supermassive black hole masses.

astro-ph.GA↗

arXiv2019

A galaxy classification grid that better recognises early-type galaxy morphology

A modified galaxy classification scheme for local galaxies is presented. It builds upon the Aitken-Jeans nebula sequence, by expanding the Jeans-Hubble tuning fork diagram, which itself contained key ingredients from Curtis and Reynolds. The two-dimensional grid of galaxy morphological types presented here, with elements from de Vaucouleurs' three-dimensional classification volume, has an increased emphasis on the often overlooked bars and continua of disc sizes in early-type galaxies - features not fully captured by past tuning forks, tridents, or combs. The grid encompasses nuclear discs in elliptical (E) galaxies, intermediate-scale discs in ellicular (ES) galaxies, and large-scale discs in lenticular (S0) galaxies, while the E4-E7 class is made redundant given that these galaxies are lenticular galaxies. Today, these disc structures continue to be neglected, or surprise researchers, perhaps partly due to our indoctrination to galaxy morphology through the tuning fork diagram. To better understand the past and present classification schemes - whose origins reside in solar/planetary formation models - a holistic overview is given. This provides due credit to some of the lesser known pioneers, presents some rationale for the grid, and reveals the incremental nature of, and some of the lesser known connections in, the field of galaxy morphology.

astro-ph.GA↗

arXiv2019

A Consistent Set of Empirical Scaling Relations for Spiral Galaxies: The $(v_{\rm max},\,M_{\rm DM})$-$(σ_0,\,M_{\rm BH},\,ϕ)$ Relations

Using the latest sample of 48 spiral galaxies having a directly measured supermassive black hole mass, $M_{BH}$, we determine how the maximum disk rotational velocity, $v_{max}$ (and the implied dark matter halo mass, $M_{DM}$), correlates with the (i) $M_{BH}$, (ii) central velocity dispersion, $σ_0$, and (iii) spiral-arm pitch angle, $ϕ$. We find that $M_{BH}\propto v_{max}^{10.62\pm1.37}\propto M_{DM}^{4.35\pm0.66}$, significantly steeper than previously reported, and with a root mean square scatter ($0.58$ dex) similar to that about the $M_{BH}$-$σ_0$ relation for spiral galaxies - in stark disagreement with claims that $M_{BH}$ does not correlate with disks. Moreover, this $M_{BH}$-$v_{max}$ relation is consistent with the unification of the Tully-Fisher relation (involving the total stellar mass, $M_{*,tot}$) and the steep $M_{BH}\propto M_{*,tot}^{3.05\pm0.53}$ relation observed in spiral galaxies. We also find that $σ_0\propto v_{max}^{1.55\pm0.25}\propto M_{DM}^{0.63\pm0.11}$, consistent with past studies connecting stellar bulges (with $σ_0\gtrsim100\,{\rm km\,s}^{-1}$), dark matter halos, and a nonconstant $v_{max}/σ_0$ ratio. Finally, we report that $\tan|ϕ|\propto(-1.18\pm0.19)\log{v_{max}}\propto(-0.48\pm0.09)\log M_{DM}$, providing a novel formulation between the geometry (i.e., the logarithmic spiral-arm pitch angle) and kinematics of spiral galaxy disks. While the $v_{max}$-$ϕ$ relation may facilitate distance estimations to face-on spiral galaxies through the Tully-Fisher relation and using $ϕ$ as a proxy for $v_{max}$, the $M_{DM}$-$ϕ$ relation provides a path for determining dark matter halo masses from imaging data alone. Furthermore, based on a spiral galaxy sample size that is double the size used previously, the self-consistent relations presented here provide dramatically revised constraints for theory and simulations.

astro-ph.GA↗

arXiv2019

Expected intermediate mass black holes in the Virgo cluster. II. Late-type galaxies

The Chandra X-ray Observatory's Cycle 18 Large Program titled "Spiral galaxies of the Virgo Cluster" will image 52 galaxies with the ACIS-S detector. Combined with archival data for an additional 22 galaxies, this will represent the complete sample of 74 spiral galaxies in the Virgo cluster with star-formation rates $\gtrsim$ 0.3 $M_{\odot}$/yr. Many of these galaxies are expected to have an active nucleus, signalling the presence of a central black hole. In preparation for this survey, we predict the central black hole masses using the latest black hole scaling relations based on spiral arm pitch angle $ϕ$, velocity dispersion $σ$, and total stellar mass $M_{\rm *,galaxy}$. With a focus on intermediate mass black holes ($10^2<M_{\rm bh}/M_{\odot}<10^5$), we highlight NGC 4713 and NGC 4178, both with $M_{\rm bh}\approx10^3$-$10^4$ (an estimate which is further supported in NGC 4178 by its nuclear star cluster mass). From Chandra archival data, we find that both galaxies have a point-like nuclear X-ray source, with unabsorbed 0.3-10 keV luminosities of a few times 10$^{38}$ erg/s. In NGC 4178, the nuclear source has a soft, probably thermal, spectrum consistent with a stellar-mass black hole in the high/soft state, while no strong constraints can be derived for the nuclear emission of NGC 4713. In total, 33 of the 74 galaxies are predicted to have $M_{\rm bh}<(10^5$-$10^6)$ $M_{\odot}$, and several are consistently predicted, via three methods, to have masses of $10^4$-$10^5\,M_{\odot}$, such as IC 3392, NGC 4294 and NGC 4413. We speculate that a sizeable population of IMBHs may reside in late-type spiral galaxies with low stellar mass ($M_{\rm *,galaxy}\lesssim10^{10}\,M_{\odot}$).

astro-ph.GA↗

arXiv2019

Black Hole Mass Scaling Relations for Early-Type Galaxies: $M_{BH}$-$M_{,sph}$ and $M_{BH}$-$M_{,gal}$

Analyzing a sample of 84 early-type galaxies with directly-measured super-massive black hole masses---nearly doubling the sample size of such galaxies with multi-component decompositions---a symmetric linear regression on the reduced (merger-free) sample of 76 galaxies reveals $M_{BH}\propto M_{*,sph}^{1.27\pm 0.07}$ with a total scatter of $Δ_{rms}=$ 0.52 dex in the $\log(M_{BH})$ direction. However, and importantly, we discover that the ES/S0-type galaxies with disks are offset from the E-type galaxies by more than a factor of ten in their $M_{BH}/M_{*,sph}$ ratio, with ramifications for formation theories, simulations, and some virial factor measurements used to convert AGN virial masses into $M_{BH}$. Separately, each population follows a steeper relation with slopes of $1.86\pm0.20$ and $1.90\pm0.20$, respectively. The offset mass ratio is mainly due to the exclusion of the disk mass, with the two populations offset by only a factor of two in their $M_{BH}/M_{*,gal}$ ratio in the $M_{BH}$-$M_{*,gal}$ diagram where $M_{BH}\propto M_{*,gal}^{1.8\pm 0.2}$ and $Δ_{rms}=0.6\pm 0.1$ dex depending on the sample. For $M_{BH} \gtrsim 10^7 M_{\odot}$, we detect no significant bend nor offset in either the $M_{BH}$-$M_{*,sph}$ or $M_{BH}$-$M_{*,gal}$ relations due to barred versus non-barred, or core-Sérsic versus Sérsic, early-type galaxies. For reference, the ensemble of late-type galaxies (which invariably are Sérsic galaxies) follow $M_{BH}$-$M_{*,sph}$ and $M_{BH}$-$M_{*,gal}$ relations with slopes equal to $2.16\pm 0.32$ and $3.05\pm 0.70$, respectively. Finally, we provide some useful conversion coefficients, $\upsilon$, accounting for the different stellar mass-to-light ratios used in the literature, and we report the discovery of a local, compact massive spheroid in NGC 5252.

astro-ph.GA↗

arXiv2019

Black Hole Mass Scaling Relations for Spiral Galaxies. II. $M_{\rm BH}$-$M_{\rm ,tot}$ and $M_{\rm BH}$-$M_{\rm ,disk}$

Black hole mass ($M_{BH}$) scaling relations are typically derived using the properties of a galaxy's bulge and samples dominated by (high-mass) early-type galaxies. Studying late-type galaxies should provide greater insight into the mutual growth of black holes and galaxies in more gas-rich environments. We have used 40 spiral galaxies to establish how $M_{BH}$ scales with both the total stellar mass ($M_{*,tot}$) and the disk's stellar mass, having measured the spheroid (bulge) stellar mass ($M_{*,sph}$) and presented the $M_{BH}$-$M_{*,sph}$ relation in Paper I. The relation involving $M_{*,tot}$ may be beneficial for estimating $M_{BH}$ either from pipeline data or at higher redshift, conditions that are not ideal for the accurate isolation of the bulge. A symmetric Bayesian analysis finds $\log\left(M_{BH}/M_{\odot}\right)=\left(3.05_{-0.49}^{+0.57}\right)\log\left\{M_{*,tot}/[\upsilon(6.37\times10^{10}\,M_{\odot})]\right\}+(7.25_{-0.14}^{+0.13})$. The scatter from the regression of $M_{BH}$ on $M_{*,tot}$ is 0.66 dex; compare 0.56 dex for $M_{BH}$ on $M_{*,sph}$ and $0.57$ dex for $M_{BH}$ on $σ_*$. The slope is $>2$ times that obtained using core-Sérsic early-type galaxies, echoing a similar result involving $M_{*,sph}$, and supporting a varied growth mechanism among different morphological types. This steeper relation has consequences for galaxy/black hole formation theories, simulations, and predicting black hole masses. We caution that (i) an $M_{BH}$-$M_{*,tot}$ relation built from a mixture of early- and late-type galaxies will find an arbitrary slope of approximately 1-3, with no physical meaning beyond one's sample selection, and (ii) evolutionary studies of the $M_{BH}$-$M_{*,tot}$ relation need to be mindful of the galaxy types included at each epoch. We additionally update the $M_{*,tot}$-($\textit{face-on}$ spiral arm pitch angle) relation.

astro-ph.GA↗

arXiv2019

Black Hole Mass Scaling Relations for Spiral Galaxies. I. $M_{\rm BH}$-$M_{\rm *,sph}$

The (supermassive black hole mass, $M_\text{BH}$)-(bulge stellar mass, $M_{\rm*,sph}$) relation is, obviously, derived using two quantities. We endeavor to provide accurate values for the latter via detailed multicomponent galaxy decompositions for the current full sample of 43 spiral galaxies having directly measured $M_\text{BH}$ values; 35 of these galaxies have been alleged to contain pseudobulges, 21 have water maser measurements, and three appear bulgeless. This more than doubles the previous sample size of spiral galaxies with a finessed image analysis. We have analyzed near-infrared images, accounting for not only the bulge, disk (exponential, truncated, or inclined), and bar but also for spiral arms and rings and additional central components (active galactic nuclei (AGNs), etc.). A symmetric Bayesian analysis finds $\log\left(M_\text{BH}/M_{\odot}\right)=\left(2.44_{-0.31}^{+0.35}\right)\log\left\{M_{\rm*,sph}/[\upsilon(1.15\times10^{10}\,M_{\odot})]\right\}+(7.24\pm0.12)$, with $\upsilon$ a stellar mass-to-light ratio term. The level of scatter equals that about the $M_{\rm BH}$-$σ_*$ relation. The nonlinear slope rules out the idea that many mergers, coupled with the central limit theorem, produced this scaling relation, and it corroborates previous observational studies and simulations, which have reported a near-quadratic slope at the low-mass end of the $M_\text{BH}$-$M_{\rm*,sph}$ diagram. Furthermore, bulges with AGNs follow this relation; they are not offset by an order of magnitude, and models that have invoked AGN feedback to establish a linear $M_{\rm BH}$-$M_{\rm*,sph}$ relation need revisiting. We additionally present an updated $M_\text{BH}$-(Sérsic index, $n_\text{sph}$) relation for spiral galaxy bulges with a comparable level of scatter and a new $M_{\rm*,sph}$-(spiral-arm pitch angle, $ϕ$) relation.

astro-ph.GA↗

arXiv2018

Expected intermediate-mass black holes in the Virgo cluster. I. Early-type galaxies

We expand upon the AMUSE-Virgo survey which imaged 100 early-type Virgo cluster galaxies with the Chandra X-ray Observatory, and we place an emphasis on potential intermediate mass black holes (IMBHs). Virgo early-type galaxies with absolute magnitudes $\mathfrak{M}_B\gtrsim-20.5$ mag have $B$-band luminosities that scale with the square of the stellar velocity dispersion: $L_B\proptoσ^2$. We show that the non-linear `super-quadratic' relation $M_{\rm bh}\propto L_B^2$-$L_B^{2.5}$ from Graham & Scott yields black hole masses, $M_{\rm bh}$, that agree with the $M_{\rm bh}$-$σ$ relation down to at least $M_{\rm bh}=10^4\,M_{\odot}$. We predict that 30 of the 100 galaxies have $M_{\rm bh}\le10^5\,M_{\odot}$, with IC3602 having $M_{\rm bh}=10^4\,M_{\odot}$ and IC3633 having $M_{\rm bh}=$(6-8)$\times10^3\,M_{\odot}$. We additionally revise the black hole Eddington ratios and their scaling with black hole mass, and report a point-like Chandra source at the nucleus of five additional galaxies (NGC4382, NGC4387, NGC4417, NGC4467, and NGC4472). Moreover, three of the galaxies predicted here to host an IMBH have a point-like Chandra source near their nucleus: IC3442 ($M_{\rm bh}=2\times10^5\,M_{\odot}$); IC3492 ($M_{\rm bh}=5\times10^4\,M_{\odot}$); and IC3292 ($M_{\rm bh}=6\times10^4\,M_{\odot}$). Furthermore, IC3442 and IC3292 host a nuclear star cluster that is expected to house an IMBH. Finally, we present the ($B-K$)-$\mathfrak{M}_K$ colour-magnitude diagram and discuss the implications for the $M_{\rm bh}$-$L_K$ and $M_{\rm bh}$-$M_{\rm *,galaxy}$ relations, revealing why stripped galaxies, especially rare compact elliptical galaxies, should be excluded from $M_{\rm bh}$-$L$ and $M_{\rm bh}$-$M_{\rm *,galaxy}$ scaling relations.

astro-ph.HE↗

arXiv2018

Updating the (Supermassive Black Hole Mass) - (Spiral Arm Pitch Angle) Relation: A Strong Correlation for Galaxies with Pseudobulges

We have conducted an image analysis of the (current) full sample of 44 spiral galaxies with directly measured supermassive black hole (SMBH) masses, $M_{\rm BH}$, to determine each galaxy's logarithmic spiral arm pitch angle, $ϕ$. For predicting black hole masses, we have derived the relation: $\log({M_{\rm BH}/{\rm M_{\odot}}}) = (7.01\pm0.07) - (0.171\pm0.017)[|ϕ|-15°]$. The total root mean square scatter associated with this relation is 0.43 dex in the $\log{M_{\rm BH}}$ direction, with an intrinsic scatter of $0.33\pm0.08$ dex. The $M_{\rm BH}$-$ϕ$ relation is therefore at least as accurate at predicting SMBH masses in spiral galaxies as the other known relations. By definition, the existence of an $M_{\rm BH}$-$ϕ$ relation demands that the SMBH mass must correlate with the galaxy discs in some manner. Moreover, with the majority of our sample (37 of 44) classified in the literature as having a pseudobulge morphology, we additionally reveal that the SMBH mass correlates with the large-scale spiral pattern and thus the discs of galaxies hosting pseudobulges. Furthermore, given that the $M_{\rm BH}$-$ϕ$ relation is capable of estimating black hole masses in bulge-less spiral galaxies, it therefore has great promise for predicting which galaxies may harbour intermediate-mass black holes (IMBHs, $M_{\rm BH}<10^5$ ${\rm M_{\odot}}$). Extrapolating from the current relation, we predict that galaxies with $|ϕ| \geq 26.7°$ should possess IMBHs.

astro-ph.GA↗

arXiv2017

Galaxy And Mass Assembly (GAMA): Blue spheroids within 87 Mpc

In this paper we test if nearby blue spheroid (BSphs) galaxies may become the progenitors of star-forming spiral galaxies or passively-evolving elliptical galaxies. Our sample comprises 428 galaxies of various morphologies in the redshift range 0.002<z<0.02 (8-87 Mpc) with panchromatic data from the Galaxy and Mass Assembly survey. We find that BSph galaxies are structurally (mean effective surface brightness, effective radius) very similar to their passively-evolving red counterparts. However, their star-formation and other properties such as colour, age and metallicity are more like star-forming spirals than spheroids (ellipticals and lenticulars). We show that BSph galaxies are statistically distinguishable from other spheroids as well as spirals in the multi-dimensional space mapped by luminosity-weighted age, metallicity, dust mass and specific star formation rate. We use HI data to reveal that some of the BSphs are (further) developing their disks, hence their blue colours. They may eventually become spiral galaxies --- if sufficient gas accretion occurs --- or more likely fade into low-mass red galaxies.

astro-ph.GA↗

arXiv2017

Building the peanut: simulations and observations of peanut-shaped structures and ansae in face-on disk galaxies

(X/peanut)-shaped features observed in a significant fraction of disk galaxies are thought to have formed from vertically buckled bars. Despite being three dimensional structures, they are preferentially detected in near edge-on projection. Only a few galaxies are found to have displayed such structures when their disks are relatively face-on - suggesting that either they are generally weak in face-on projection or many may be hidden by the light of their galaxy's face-on disk. Here we report on three (collisionless) simulated galaxies displaying peanut-shaped structures when their disks are seen both face-on and edge-on - resembling a three-dimensional peanut or dumbbell. Furthermore, these structures are accompanied by ansae and an outer ring at the end of the bar --- as seen in real galaxies such as IC~5240. The same set of quantitative parameters used to measure peanut structures in real galaxies have been determined for the simulated galaxies, and a broad agreement is found. In addition, the peanut length grows in tandem with the bar, and is a maximum at half the length of the bar. Beyond the cutoff of these peanut structures, towards the end of the bar, we discover a new positive/negative feature in the $B_6$ radial profile associated with the isophotes of the ansae/ring. Our simulated, self-gravitating, three-dimensional peanut structures display cylindrical rotation even in the near-face-on disk projection. In addition, we report on a kinematic pinch in the velocity map along the bar minor-axis, matching that seen in the surface density map.

astro-ph.GA↗

arXiv2017

Galaxy And Mass Assembly: Automatic Morphological Classification of Galaxies Using Statistical Learning

We apply four statistical learning methods to a sample of $7941$ galaxies ($z<0.06$) from the Galaxy and Mass Assembly (GAMA) survey to test the feasibility of using automated algorithms to classify galaxies. Using $10$ features measured for each galaxy (sizes, colours, shape parameters \& stellar mass) we apply the techniques of Support Vector Machines (SVM), Classification Trees (CT), Classification Trees with Random Forest (CTRF) and Neural Networks (NN), returning True Prediction Ratios (TPRs) of $75.8\%$, $69.0\%$, $76.2\%$ and $76.0\%$ respectively. Those occasions whereby all four algorithms agree with each other yet disagree with the visual classification (`unanimous disagreement') serves as a potential indicator of human error in classification, occurring in $\sim9\%$ of ellipticals, $\sim9\%$ of Little Blue Spheroids, $\sim14\%$ of early-type spirals, $\sim21\%$ of intermediate-type spirals and $\sim4\%$ of late-type spirals \& irregulars. We observe that the choice of parameters rather than that of algorithms is more crucial in determining classification accuracy. Due to its simplicity in formulation and implementation, we recommend the CTRF algorithm for classifying future galaxy datasets. Adopting the CTRF algorithm, the TPRs of the 5 galaxy types are : E, $70.1\%$; LBS, $75.6\%$; S0-Sa, $63.6\%$; Sab-Scd, $56.4\%$ and Sd-Irr, $88.9\%$. Further, we train a binary classifier using this CTRF algorithm that divides galaxies into spheroid-dominated (E, LBS \& S0-Sa) and disk-dominated (Sab-Scd \& Sd-Irr), achieving an overall accuracy of $89.8\%$. This translates into an accuracy of $84.9\%$ for spheroid-dominated systems and $92.5\%$ for disk-dominated systems.

astro-ph.GA↗