arXiv subjects

Benjamin L. Davis

Publications and source records attributed to Benjamin L. Davis.

At least 37 records · Page 2Linked to original sources

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)

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arXiv2020

Evidence in favour of density wave theory through star formation history maps and spatially resolved stellar clusters

Stationary Density Wave Theory predicts the existence of an age gradient across the spiral arms with a phase crossing at the co-rotation radius. Using star formation history (SFH) maps of 12 nearby spiral galaxies derived from \textsc{LIGHTNING} \citep{Eufracio:2017}, a spectral energy distribution (SED) fitting procedure, and by using \textsc{Spirality} \citep{Shield:2015} a \textsc{MATLAB}-based code which plots synthetic spiral arms over \textsc{FITS} images, we have found a gradual decrement in pitch angles with increasing age, thus providing us with evidence in favour of the Stationary Density Wave Theory. We have also used azimuthal offsets of spatially resolved stellar clusters in 3 LEGUS galaxies to observe age trends.

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arXiv2020

Determining the Co-Rotation Radii of Spiral Galaxies Using Spiral Arm Pitch Angle Measurements at Multiple Wavelengths

The spiral arms spanning disk galaxies are believed to be created by density waves that propagate through galactic disks. We present a novel method of finding the co-rotation radius where the spiral arm pattern speed matches the velocities of the stars within the disk. Our method uses an image-overlay technique, which involves tracing the arms of spiral galaxies on images observed in different wavelengths. Density wave theory predicts that spiral arms observed from different wavelengths show a phase crossing at the co-rotation radius. For the purpose of this study, 20 nearby galaxies were analyzed in four different wavelengths with pitch angle measurements performed by two independent methods. We used optical wavelength images ($B$-band 440nm), two infrared wavelength images provided by Spitzer (3.6$μ$m and 8$μ$m) and ultraviolet images from GALEX (1350Å, 1750Å). The results were compared and verified with other records found in the literature. We then found rotation curve data for six of our galaxies and used our co-rotation radii estimates to measure the time that would elapse between star formation and moving to their observed positions in the $B$-band spirals. The average time lapse for this motion was found to be $\sim$ 50 Myr. The success of this new method of finding the co-rotation radius confirms density wave theory in a very direct way.

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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)

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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.

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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 ($M_{\rm *,galaxy}\lesssim10^{10}\,M_{\odot}$).

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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.

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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.

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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.

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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.

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arXiv2018

The Black Hole Mass Function Derived from Local Spiral Galaxies

We present our determination of the nuclear supermassive black hole (SMBH) mass function for spiral galaxies in the Local Universe, established from a volume-limited sample consisting of a statistically complete collection of the brightest spiral galaxies in the Southern Hemisphere. Our SMBH mass function agrees well at the high-mass end with previous values given in the literature. At the low-mass end, inconsistencies exist in previous works that still need to be resolved, but our work is more in line with expectations based on modeling of SMBH evolution. This low-mass end of the spectrum is critical to our understanding of the mass function and evolution of SMBHs since the epoch of maximum quasar activity. A luminosity distance $\leq$ 25.4 $Mpc$ and an absolute B-band magnitude $\leq$ -19.12 define the sample. These limits define a sample of 140 spiral galaxies, with 128 measurable pitch angles to establish the pitch angle distribution for this sample. This pitch angle distribution function may be useful in the study of the morphology of late-type galaxies. We then use an established relationship between the pitch angle and the mass of the central SMBH in a host galaxy in order to estimate the mass of the 128 respective SMBHs in this sample. This result effectively gives us the distribution of mass for SMBHs residing in spiral galaxies over a lookback time $\leq$ 82.1 $h_{67.77}^{-1}$ $Myr$ and contained within a comoving volume of 3.37 $\times$ $10^4$ $h_{67.77}^{-3}$ $Mpc^3$. We estimate the density of SMBHs residing in spiral galaxies in the Local Universe is $5.54_{-2.73}^{+6.55}$ $\times$ $10^4$ $h_{67.77}^3$ $M_{\odot}$ $Mpc^{-3}$. Thus, our derived cosmological SMBH mass density for spiral galaxies is $Ω_{BH} = 4.35_{-2.15}^{+5.14}$ $\times$ $10^{-7}$ $h_{67.77}$.

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arXiv2017

A Fundamental Plane of Spiral Structure in Disk Galaxies

Spiral structure is the most distinctive feature of disk galaxies and yet debate persists about which theory of spiral structure is the correct one. Many versions of the density wave theory demand that the pitch angle is uniquely determined by the distribution of mass in the bulge and disk of the galaxy. We present evidence that the tangent of the pitch angle of logarithmic spiral arms in disk galaxies correlates strongly with the density of neutral atomic hydrogen in the disk and with the central stellar bulge mass of the galaxy. These three quantities, when plotted against each other, form a planar relationship which, we argue should be fundamental to our understanding of spiral structure in disk galaxies. We further argue that any successful theory of spiral structure must be able to explain this relationship.

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arXiv2017

Searching for Intermediate Mass Black Holes in galaxies with Low Luminosity AGN: A multiple-method approach

Aims: This work is the first stage of a campaign to search for IMBHs, in low luminosity AGN (LLAGN) and dwarf galaxies. An additional, and equally important, aim of this pilot study is to investigate the consistency between the predictions of several BH scaling relations and the fundamental plane of black hole activity (FP-BH). Methods: We use X-ray and radio luminosity relations in accreting BHs, along with the latest scaling relations between the mass of the central black hole (MBH) and the properties of its host spheroid, to predict MBH in seven LLAGN, that were previously reported to be in the IMBH regime. Namely, we use the recently re-evaluated MBH - Msph (Msph : spheroid absolute magnitude at 3.6 microm) scaling relation for spiral galaxies, the MBH - nsph (nsph : major axis Sersic index of the bulge) relation, the MBH - PA (PA: pitch angle) relation and the FP-BH for weakly accreting BHs, to independently estimate MBH in all seven galaxies. Results: We find that all LLAGN in our list have low-mass central black holes - with log MBH/Msol~6.5 on average - but they are, not IMBHs. All 4 methods used predicted consistent BH masses, in the 1sigma range. Furthermore, we report that, in contrast to previous classification, galaxy NGC 4470 is bulge-less, and cast doubts on the AGN classification of NGC 3507. Conclusions: We find that our latest, state-of-the-art techniques for bulge magnitude & Sersic index computations and the most recent updates of the MBH - Lsph, MBH - nsph , MBH - PA relations and the FP-BH produce consistent results in the low mass regime. We establish a multiple method approach for predicting BH masses in the regime where their spheres-of- grav. influence cannot be spatially resolved. Our approach mitigates against outliers from any one relation and provides a more robust average prediction. We will use our new method to revisit more IMBH candidates in LLAGN

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arXiv2016

Strong Evidence for the Density-wave Theory of Spiral Structure in Disk Galaxies

The density-wave theory of galactic spiral-arm structure makes a striking prediction that the pitch angle of spiral arms should vary with the wavelength of the galaxy's image. The reason is that stars are born in the density wave but move out of it as they age. They move ahead of the density wave inside the co-rotation radius, and fall behind outside of it, resulting in a tighter pitch angle at wavelengths that image stars (optical and near-infrared) than those that are associated with star formation (far-infrared and ultraviolet). In this study we combined large sample size with wide range of wavelengths, from the ultraviolet to the infrared to investigate this issue. For each galaxy we used an optical wavelength image (B-band: 445 nm) and images from the Spitzer Space Telescope at two infrared wavelengths (infrared: 3.6 and 8.0 μm) and we measured the pitch angle with the 2DFFT and Spirality codes. We find that the B-band and 3.6 μm images have smaller pitch angles than the infrared 8.0 μm image in all cases, in agreement with the prediction of density-wave theory. We also used images in the ultraviolet from Galaxy Evolution Explorer, whose pitch angles agreed with the measurements made at 8 μm.

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arXiv2016

The local black hole mass function derived from the M_{BH}-P and the M_{BH}-n relations

We present a determination of the supermassive black hole (SMBH) mass function for early- and late-type galaxies in the nearby universe (z<0.0057), established from a volume-limited sample consisting of a statistically complete collection of the brightest spiral galaxies in the southern hemisphere. The sample is defined by limiting luminosity (redshift-independent) distance, D_L=25.4 Mpc, and a limiting absolute B-band magnitude, M_B=-19.12. These limits define a sample of 140 spiral, 30 elliptical (E), and 38 lenticular (S0) galaxies. We established the Sersic index distribution for early-type (E/S0) galaxies in our sample. Davis et al. (2014) established the pitch angle distribution for their sample, which is identical to our late-type (spiral) galaxy sample. We then used the pitch angle and the Sersic index distributions in order to estimate the SMBH mass function for our volume-limited sample. The observational simplicity of our approach relies on the empirical relation between the mass of the central (SMBH) and the Sersic index (Graham et al. 2007) for an early-type galaxy or the logarithmic spiral arm pitch angle (Berrier et al. 2013) for a spiral galaxy. Our SMBH mass function agrees well at the high-mass end with previous values in the literature. At the low-mass end, while inconsistencies exist in previous works that still need to be resolved, our work is more in line with expectations based on modeling of black hole evolution.

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arXiv2016

Spirality: A Novel Way to Measure Spiral Arm Pitch Angle

We present the MATLAB code Spirality, a novel method for measuring spiral arm pitch angles by fitting galaxy images to spiral templates of known pitch. Computation time is typically on the order of 2 minutes per galaxy, assuming at least 8 GB of working memory. We tested the code using 117 synthetic spiral images with known pitches, varying both the spiral properties and the input parameters. The code yielded correct results for all synthetic spirals with galaxy-like properties. We also compared the code's results to two-dimensional Fast Fourier Transform (2DFFT) measurements for the sample of nearby galaxies defined by DMS PPak. Spirality's error bars overlapped 2DFFT's error bars for 26 of the 30 galaxies. The two methods' agreement correlates strongly with galaxy radius in pixels and also with i-band magnitude, but not with redshift, a result that is consistent with at least some galaxies' spiral structure being fully formed by z=1.2, beyond which there are few galaxies in our sample. The Spirality code package also includes GenSpiral, which produces FITS images of synthetic spirals, and SpiralArmCount, which uses a one-dimensional Fast Fourier Transform to count the spiral arms of a galaxy after its pitch is determined. The code package is freely available online; see Comments for URL.

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arXiv2014

Constraining dark matter halo profiles and galaxy formation models using spiral arm morphology. II. Dark and stellar mass concentrations for 13 nearby face-on galaxies

We investigate the use of spiral arm pitch angles as a probe of disk galaxy mass profiles. We confirm our previous result that spiral arm pitch angles (P) are well correlated with the rate of shear (S) in disk galaxy rotation curves. We use this correlation to argue that imaging data alone can provide a powerful probe of galactic mass distributions out to large look-back times. We then use a sample of 13 galaxies, with Spitzer 3.6-$μ$m imaging data and observed H$α$ rotation curves, to demonstrate how an inferred shear rate coupled with a bulge-disk decomposition model and a Tully-Fisher-derived velocity normalization can be used to place constraints on a galaxy's baryon fraction and dark matter halo profile. Finally we show that there appears to be a trend (albeit a weak correlation) between spiral arm pitch angle and halo concentration. We discuss implications for the suggested link between supermassive black hole (SMBH) mass and dark halo concentration, using pitch angle as a proxy for SMBH mass.

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arXiv2013

Further Evidence for a Supermassive Black Hole Mass - Pitch Angle Relation

We present new and stronger evidence for a previously reported relationship between galactic spiral arm pitch angle P (a measure of the tightness of spiral structure) and the mass M_BH of a disk galaxy's nuclear supermassive black hole (SMBH). We use an improved method to accurately measure the spiral arm pitch angle in disk galaxies to generate quantitative data on this morphological feature for 34 galaxies with directly measured black hole masses. We find a relation of log(M/M_sun) = (8.21 +/- 0.16) - (0.062 +/- 0.009)P. This method is compared with other means of estimating black hole mass to determine its effectiveness and usefulness relative to other existing relations. We argue that such a relationship is predicted by leading theories of spiral structure in disk galaxies, including the density wave theory. We propose this relationship as a tool for estimating SMBH masses in disk galaxies. This tool is potentially superior when compared to other methods for this class of galaxy and has the advantage of being unambiguously measurable from imaging data alone.

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