X-shaped or peanut-shaped (X/P) bulges are observed in more than 40% of (nearly) edge-on disc galaxies, though to date a robust method to quantify them is lacking. Using Fourier harmonics to describe the deviation of galaxy isophotes from ellipses, we demonstrate with a sample of 11 such galaxies (including NGC 128) that the sixth Fourier component (B 6 ) carries physical meaning by tracing this X/P structure. We introduce five quantitative diagnostics based on the radial B 6 profile, namely: its 'peak' amplitude (Π max ); the (projected major-axis) 'length' where this peak occurs (R Π ,max ); its vertical 'height' above the disc plane (z Π ,max ); a measure of the B 6 profile's integrated 'strength' (S Π ); and the B 6 peak 'width' (W Π ). We also introduce different 'classes' of B 6 profile shape. Furthermore, we convincingly detect and measure the properties of multiple (nested) X/P structures in individual galaxies which additionally display the signatures of multiple bars in their surface brightness profiles, thus consolidating further the scenario in which peanuts are associated with bars. We reveal that the peanut parameter space ('length', 'strength' and 'height') for real galaxies is not randomly populated, but the three metrics are inter-correlated (both in kpc and disc scale-length h). Additionally, the X/P 'length' and 'strength' appear to correlate with (v rot /σ ), lending further support to the notion that peanuts 'know' about the galactic disc in which they reside. Such constraints are important for numerical simulations, as they provide a direct link between peanuts and their host disc. Our diagnostics reveal a spectrum of X/P properties and could provide a means of distinguishing between different peanut formation scenarios discussed in the literature. Moreover, nested peanuts, as remnants of bar buckling events, can provide insights into the disc and bar instability history.

This work introduces a new fitting formalism for isophotes which enables more accurate modelling of galaxies with non-elliptical shapes, such as disk galaxies viewed edge-on or galaxies with Xshaped/peanut bulges. Within this scheme, the angular parameter which defines quasi-elliptical isophotes is transformed from the commonly used, but inappropriate, polar co-ordinate to the 'eccentric anomaly'. This provides a superior description of deviations from ellipticity, better capturing the true isophotal shape. Furthermore, this makes it possible to accurately recover both the surface brightness profile, using the correct azimuthally-averaged isophote, and the two-dimensional model of any galaxy: the hitherto ubiquitous, but artificial, cross-like features in residual images are completely removed. The formalism has been implemented into the IRAF tasks Ellipse and Bmodel to create the new tasks 'Isofit', and 'Cmodel'. The new tools are demonstrated here with application to five galaxies, chosen to be representative case-studies for several areas where this technique makes it possible to gain new scientific insight. Specifically: properly quantifying boxy/disky isophotes via the fourth harmonic order in edge-on galaxies, quantifying X-shaped/peanut bulges, higher-order Fourier moments for modelling bars in disks, and complex isophote shapes. Higher order (n > 4) harmonics now become meaningful and may correlate with structural properties, as boxyness/diskyness is known to do. This work also illustrates how the accurate construction, and subtraction, of a model from a galaxy image facilitates the identification and recovery of over-lapping sources such as globular clusters and the optical counterparts of X-ray sources.

The mass scaling relation between supermassive black holes and their host spheroids has previously been described by a quadratic or steeper relation at low masses (10 5 < M bh /M 10 7 ). How this extends into the realm of intermediate mass black holes (10 2 < M bh /M < 10 5 ) is not yet clear, although for the barred Sm galaxy LEDA 87300, Baldassare et al. have recently reported a nominal virial mass M bh = 5 × 10 4 M residing in a 'spheroid' of stellar mass equal to 6.3 × 10 8 M . We point out, for the first time, that LEDA 87300 therefore appears to reside on the near-quadratic M bh -M sph, * relation. However, Baldassare et al. modelled the bulge and bar as the single spheroidal component of this galaxy. Here we perform a 3-component bulge+bar+disk decomposition and find a bulge luminosity which is 7.7 times fainter than the published 'bulge' luminosity. After correcting for dust, we find that M bulge = 0.9 × 10 8 M and M bulge /M disk = 0.04 -which is now in accord with ratios typically found in Scd-Sm galaxies. We go on to discuss slight revisions to the stellar velocity dispersion (40 ± 11 km s −1 ) and black hole mass (M bh = 2.9 +6.7 −2.3 × 10 4 f 2.3 M ) and show that LEDA 87300 remains consistent with the M bh -σ relation, and also the near-quadratic M bh -M sph, * relation when using the reduced bulge mass. LEDA 87300 therefore offers the first support for the rapid but regulated (near-quadratic) growth of black holes, relative to their host bulge/spheroid, extending into the domain of intermediate mass black holes.

The nature, size and orientation of the dominant structural components in the Milky Way's inner ∼ 4 kpc -specifically the bulge and bar -have been the subject of conflicting interpretations in the literature. We present a different approach to inferring the properties of the long bar which extends beyond the inner bulge, via the information encoded in the Galaxy's X/peanut (X/P)-shaped structure. We perform a quantitative analysis of the X/P feature seen in wise wide-field imaging at 3.4 µm and 4.6 µm. We measure the deviations of the isophotes from pure ellipses, and quantify the X/P structure via the radial profile of the Fourier n = 6 harmonic (cosine term B 6 ). In addition to the vertical height and integrated 'strength' of the X/P instability, we report an intrinsic radius of R Π ,int = 1.67 ± 0.27 kpc, and an orientation angle of α = 37•+7• −10 • with respect to our line-of-sight to the Galactic Centre. Based on X/P structures observed in other galaxies, we make three assumptions: (i) the peanut is intrinsically symmetric, (ii) the peanut is aligned with the long Galactic bar, and (iii) their sizes are correlated. Thus the implication for the Galactic bar is that it is oriented at the same 37• angle and has an expected radius of ≈ 4.2 kpc, but possibly as low as ≈ 3.2 kpc. We further investigate how the Milky Way's X/P structure compares with other analogues, and find that the Galaxy is broadly consistent with our recently established scaling relations, though with a moderately stronger peanut instability than expected. We additionally perform a photometric decomposition of the Milky Way's major axis surface brightness profile, accounting for spiral structure, and determine an average disc scale length of h = 2.54 ± 0.16 kpc in the wise bands, in good agreement with the literature.

I introduce Profiler, a new, user-friendly program written in Python and designed to analyse the radial surface brightness profiles of galaxies. With an intuitive graphical user interface, Profiler can accurately model a wide range of galaxies and galaxy components, such as elliptical galaxies, the bulges of spiral and lenticular galaxies, nuclear sources, discs, bars, rings, spiral arms, etc., with a variety of parametric functions routinely employed in the field (Sérsic, core-Sérsic, exponential, Gaussian, Moffat and Ferrers). In addition to these, Profiler can employ the broken exponential model (relevant for disc truncations or antitruncations) and two special cases of the edge-on disc model: namely along the major axis (in the disc plane) and along the minor axis (perpendicular to the disc plane). Profiler is optimised to work with galaxy light profiles obtained from isophotal measurements which capture radial gradients in the ellipticity, position angle and Fourier harmonic profiles of the isophotes, and are thus often better at capturing the total light than two-dimensional image-fitting programs. Additionally, the one-dimensional approach is generally less computationally expensive and more stable. In Profiler, the convolution of either circular or elliptical models with the point spread function is performed in two-dimensions, and offers a choice between Gaussian, Moffat or a user-provided data vector (a table of intensity values as a function of radius) for the point spread function. I demonstrate Profiler's features and operation by decomposing three case-study galaxies: the cored elliptical galaxy NGC 3348, the nucleated dwarf Seyfert I galaxy Pox 52, and NGC 2549, a structurally complex, double-barred galaxy which additionally displays a Type II truncated disc viewed edge-on.Profiler is freely available at https://github.com/BogdanCiambur/PROFILER.

While spiral and lenticular galaxies have large-scale disks extending beyond their bulges, and most local early-type galaxies with 10 10 < M * /M < 2 × 10 11 contain a disk (e.g., ATLAS 3D ), the earlytype galaxies do possess a range of disk sizes. The edge-on, intermediate-scale disk in the 'disky elliptical' galaxy NGC 1271 has led to some uncertainty as to what is its spheroidal component. Walsh et al. reported a directly measured black hole mass of (3.09 M for this galaxy; which they remarked was an order of magnitude greater than what they expected based on their derivation of the host spheroid's luminosity. Our near-infrared image analysis supports a small embedded disk within a massive spheroidal component with M sph, * = (0.9 ± 0.2) × 10 11 M (using M * /L H = 1.4from Walsh et al.). This places NGC 1271 just 1.6-sigma above the near-linear M bh -M sph, * relation for early-type galaxies. Therefore, past speculation that there may be a systematic difference in the black hole scaling relations between compact massive early-type galaxies with intermediate-scale disks, i.e. ES galaxies such as NGC 1271, and early-type galaxies with either no substantial disk (E) or a large-scale disk (S0) is not strongly supported by NGC 1271. We additionally (i) show how ES galaxies fit naturally in the ('bulge'-to-total)-(morphological type) diagram, while noting a complication with recent revisions to the Hubble-Jeans tuning-fork diagram, (ii) caution about claims of over-massive black holes in other ES galaxies if incorrectly modelled as S0 galaxies, and (iii) reveal that the compact massive spheroid in NGC 1271 has properties similar to bright bulges in other galaxies which have grown larger-scale disks.

Selected from a sample of nine, isolated, dwarf early-type galaxies (ETGs) with the same range of kinematic properties as dwarf ETGs in clusters, we use LEDA 2108986 (CG 611) to address the Nature versus Nurture debate regarding the formation of dwarf ETGs. The presence of faint disk structures and rotation within some cluster dwarf ETGs has often been heralded as evidence that they were once late-type spiral or dwarf irregular galaxies prior to experiencing a cluster-induced transformation into an ETG. However, CG 611 also contains significant stellar rotation (≈20 km s −1 ) over its inner half-light radius (R e,maj = 0.71 kpc), and its stellar structure and kinematics resemble those of cluster ETGs. In addition to hosting a faint young nuclear spiral within a possible intermediate-scale stellar disk, CG 611 has accreted an intermediate-scale, counter-rotating gas disk. It is therefore apparent that dwarf ETGs can be built by accretion events, as opposed to disk-stripping scenarios. We go on to discuss how both dwarf and ordinary ETGs with intermediate-scale disks, whether under (de)construction or not, are not fully represented by the kinematic scaling S 0.5 = 0.5 V 2 rot + σ 2 , and we also introduce a modified spin-ellipticity diagram λ(R)-(R) with the potential to track galaxies with such disks.

In the Milky Way bulge, metal-rich stars form a strong bar and are more peanut-shaped than metal-poor stars. It has recently been claimed that this behavior is driven by the initial (i.e., before bar formation) in-plane radial velocity dispersion of these populations, rather than by their initial vertical random motions. This has led to the suggestion that a thick disk is not necessary to explain the characteristics of the Milky Way bulge. We discuss this issue again by analyzing two dissipationless N-body simulations of boxy or peanut-shaped bulges formed from composite stellar disks that consist of kinematically cold and hot stellar populations. These two models represent two extreme cases: one where all three components of the disk have a fixed vertical velocity dispersion and different in-plane radial dispersion, and another where they all have a fixed radial dispersion and different vertical random motions (thickness). This is intended to quantify the drivers of the main features that are observed in composite boxy or peanut-shaped bulges and their origin. We quantify the mapping into a boxy or peanut-shaped bulge of disk populations in these two cases, and we conclude that initial vertical random motions are as important as in-plane random motions in determining the relative contribution of cold-and hotdisk populations with height above the plane, the metallicity and age trends. Previous statements emphasizing the dominant role of in-plane motions in determining these trends are not confirmed. However, significant differences exist in the morphology and strength of the resulting boxy or peanut-shaped bulges. In particular, the model where disk populations initially have only different in-plane random motions, but similar thickness, results in a boxy or peanut-shaped bulge where all populations have a similar peanut shape, independent of their initial kinematics or metallicity. This is at odds with the trends observed in the Milky Way bulge. We discuss the reasons behind these differences, and also predict the signatures that these two extreme initial conditions would leave on the vertical age and metallicity gradients of disk stars outside the bulge region. As a consequence of this analysis, we conclude that given our current knowledge of the Milky Way bulge and of the properties of its main stellar components, a metal-poor, kinematically (radial and vertical) hot component, that is, a thick disk, is necessary in the Milky Way before bar formation. This supports the scenario that has been traced in previous works. Boxy or peanut-shaped bulges and their surrounding regions are fossil records of the conditions present at early times in disk galaxies, and by dissecting their stellar components by chemical compositions and/or age, it may be possible to reconstruct their early state.