Surface Brightness Profiles Research Articles

Distant activity of long-period comets C/2019 L3 (ATLAS) and C/2020 P3 (ATLAS)

ABSTRACT Long-period comets C/2019 L3 (ATLAS) and C/2020 P3 (ATLAS) remain active at heliocentric distance greater than 4 au. Broad-band Charge-Coupled Device (CCD) photometry of long-period comets C/2019 L3 and C/2020 P3 is analysed in this paper. The observation was obtained with three telescopes: ZEISS-1000 at Simeiz Observatory, Maksutov at Abastumani Astrophysical Observatory, and ZTSh at Crimean Astrophysical Observatory. The R-band A(0)fρ values of C/2019 L3 range from (5043 ± 244) to (13611 ± 1874) cm, and tend to decrease first and then increase. The average colour indices of C/2019 L3 are B–V = 0.75 ± 0.06, V–R = 0.28 ± 0.05, and R–I = 0.21 ± 0.05. The reddening of C/2019 L3 exhibits variations during the observational runs, ranging from (13.75 ± 1.07) to (−15.69 ± 0.37) per cent/kÅ with an average value of (0.94 ± 0.23) per cent/kÅ. It possesses a non-steady coma since the average gradient of its surface brightness profile is −1.60. For comet C/2020 P3, its R-band A(0)fρ values range from (606 ± 31) to (869 ± 20) cm, the colour indices are B–V = 1.04 ± 0.09, V–R = 0.26 ± 0.05, and R–I = 0.76 ± 0.04, and the reddening is (−6.65 ± 0.01) per cent/kÅ. The colour indices of the two comets differ from those of other long-period comets. Compared with other long-period comets, comet C/2019 L3 is very active at heliocentric distance of ∼4 au, while C/2020 P3 is moderately active at heliocentric distance of ∼7 au.

Sardinia Radio Telescope observations of the Coma cluster

ABSTRACT We present deep total intensity and polarization observations of the Coma cluster at 1.4 and 6.6 GHz performed with the Sardinia Radio Telescope. By combining the single-dish 1.4 GHz data with archival Very Large Array observations, we obtain new images of the central radio halo and of the peripheral radio relic where we properly recover the brightness from the large-scale structures. At 6.6 GHz, we detect both the relic and the central part of the halo in total intensity and polarization. These are the highest frequency images available to date for these radio sources in this galaxy cluster. In the halo, we find a localized spot of polarized signal, with fractional polarization of about 45 per cent. The polarized emission possibly extends along the north-east side of the diffuse emission. The relic is highly polarized, up to 55 per cent, as usually found for these sources. We confirm the halo spectrum is curved, in agreement with previous single-dish results. The spectral index is α = 1.48 ± 0.07 at a reference frequency of 1 GHz and varies from α ≃ 1.1, at 0.1 GHz, up to α ≃ 1.8, at 10 GHz. We compare the Coma radio halo surface brightness profile at 1.4 GHz (central brightness and e-folding radius) with the same properties of the other haloes, and we find that it has one of the lowest emissivities observed so far. Reanalysing the relic’s spectrum in the light of the new data, we obtain a refined radio Mach number of M = 2.9 ± 0.1.

Census for the rest-frame optical and UV morphologies of galaxies at z = 4–10: First phase of inside-out galaxy formation

Abstract We present the rest-frame optical and UV surface brightness (SB) profiles for 149 galaxies with Mopt < −19.4 mag at z = 4–10 (29 of which are spectroscopically confirmed with JWST NIRSpec), securing high signal-to-noise ratios of 10–135 with deep JWST NIRCam 1–$5\, \mu$m images obtained by the CEERS survey. We derive morphologies of our high-z galaxies, carefully evaluating the systematics of SB profile measurements with Monte Carlo simulations as well as the impacts of a) AGNs, b) multiple clumps including galaxy mergers, c) spatial resolution differences with previous HST studies, and d) strong emission lines, e.g., Hα and [O iii], on optical morphologies with medium-band F410M images. Conducting Sérsic profile fitting for our high-z galaxy SBs with GALFIT, we obtain effective radius ranges for optical re,opt and UV re,UV wavelengths of re, opt = 0.05–1.6 kpc and re,UV = 0.03–1.7 kpc that are consistent with previous results within large scatters in the size–luminosity relations. However, we find that the effective radius ratio, re,opt$/$re,UV, is almost unity, $1.01^{+0.35}_{-0.22}$, over z = 4–10 with no signatures of past inside-out star formation such as found at z ∼ 0–2. There are no spatial offsets exceeding 3σ between the optical and UV morphology centers in cases of no mergers, indicative of major star-forming activity only being found near mass centers of galaxies at z ≳ 4 probably experiencing the first phase of inside-out galaxy formation.

The ALMaQUEST Survey XIV: do radial molecular gas flows affect the star-forming ability of barred galaxies?

ABSTRACT We investigate whether barred galaxies are statistically more likely to harbour radial molecular gas flows and what effect those flows have on their global properties. Using 46 galaxies from the ALMA-MaNGA QUEnching and STar formation (ALMaQUEST) survey, we identify galaxies hosting optical bars using a combination of the morphological classifications in Galaxy Zoo 2 and HyperLEDA. In order to detect radial molecular gas flows, we employ full 3D kinematic modelling of the ALMaQUEST 12CO(1–0) data cubes. By combining our bar classifications with our radial bar-driven flow detections, we find that galaxies classed as barred are statistically more likely to host large-scale radial gas motions compared to their un-barred and edge-on galaxy counterparts. Moreover, the majority of barred galaxies require multicomponent surface brightness profiles in their best-fitting models, indicative of the presence of resonance systems. We find that galaxies classed as barred with radial bar-driven flows (‘barred + radial flow’ subset) have significantly suppressed global star-formation efficiencies compared to barred galaxies without radial bar-driven flows and galaxies in the other morphological sub-samples. Our ‘barred + radial flow’ subset galaxies also possess consistently centrally concentrated molecular gas distributions, with no indication of depleted gas mass fractions, suggesting that gas exhaustion is not the cause of their suppressed star formation. Furthermore, these objects have higher median gas mass surface densities in their central 1 kpc, implying that central gas enhancements do not fuel central starbursts in these objects. We propose that dynamical effects, such as shear caused by large-scale inflows of gas, act to gravitationally stabilize the inner gas reservoirs.

Strong size evolution of disc galaxies since z = 1

Our understanding of how the size of galaxies has evolved over cosmic time is based on the use of the half-light (effective) radius as a size indicator. Although the half-light radius has many advantages for structurally parameterising galaxies, it does not provide a measure of the global extent of the objects, but only an indication of the size of the region containing the innermost 50% of the galaxy’s light. Therefore, the observed mild evolution of the effective radius of disc galaxies with cosmic time is conditioned by the evolution of the central part of the galaxies rather than by the evolutionary properties of the whole structure. Expanding on recent works, we studied the size evolution of disc galaxies using the radial location of the gas density threshold for star formation as a size indicator. As a proxy to evaluate this quantity, we used the radial position of the truncation (edge) in the stellar surface mass density profiles of galaxies. To conduct this task, we selected 1048 disc galaxies with Mstellar > 1010 M⊙ and spectroscopic redshifts up to z = 1 within the HST CANDELS fields. We derived their surface brightness, colour and stellar mass density profiles. Using the new size indicator, the observed scatter of the size–mass relation (∼0.1 dex) decreases by a factor of ∼2 compared to that using the effective radius. At a fixed stellar mass, Milky Way-like (MW-like; Mstellar ∼ 5 × 1010 M⊙) disc galaxies have, on average, increased their sizes by a factor of two in the last 8 Gyr, while the surface stellar mass density at the edge position (Σedge) has decreased by more than an order of magnitude from ∼13 M⊙ pc−2 (z = 1) to ∼1 M⊙ pc−2 (z = 0). These results reflect a dramatic evolution of the outer part of MW-like disc galaxies, with an average radial growth rate of its discs of about 1.5 kpc Gyr−1.

JWST reveals a high fraction of disk breaks at 1 ≤z≤ 3

We analyzed the deconvolved surface brightness profiles of 247 massive and angularly large disk galaxies at 1 ≤ z ≤ 3 to study high-redshift disk breaks, usingF356W-band images from the Cosmic Evolution Early Release Science survey (CEERS). We found that 12.6% of these galaxies exhibit type I (exponential) profiles, 56.7% exhibit type II (down-bending) profiles, and 34.8% exhibit type III (up-bending) profiles. Moreover, we showed that galaxies that are more massive, centrally concentrated, or redder, tend to show fewer type II and more type III breaks. These fractions and the detected dependencies on galaxy properties are in good agreement with those observed in the Local Universe. In particular, the ratio of the type II disk break radius to the bar radius in barred galaxies typically peaks at a value of 2.25, perhaps due to bar-induced radial migration. However, the timescale for secular evolution may be too lengthy to explain the observed breaks at such high redshifts. Instead, violent disk instabilities may be responsible, where spiral arms and clumps torque fling out the material, leading to the formation of outer exponential disks. Our results provide further evidence for the assertion that the Hubble Sequence was already in place during these early periods.

A forward-modelling approach to overcome point spread function smearing and fit flexible models to the chemical structure of galaxies

ABSTRACT Historically, metallicity profiles of galaxies have been modelled using a radially symmetric, two-parameter linear model, which reveals that most galaxies are more metal-rich in their central regions than their outskirts. However, this model is known to yield inaccurate results when the point spread function (PSF) of a telescope is large. Furthermore, a radially symmetric model cannot capture asymmetric structures within a galaxy. In this work, we present an extension of the popular forward-modelling Python package lenstronomy, which allows the user to overcome both of these obstacles. We demonstrate the new features of this code base through two illustrative examples on simulated data. First, we show that through forward modelling, lenstronomy is able to recover accurately the metallicity gradients of galaxies, even when the PSF is comparable with the size of a galaxy, as long as the data are observed with a sufficient number of pixels. Additionally, we demonstrate how lenstronomy is able to fit irregular metallicity profiles to galaxies that are not well-described by a simple surface brightness profile. This opens up pathways for detailed investigations into the connections between morphology and chemical structure for galaxies at cosmological distances using the transformative capabilities of JWST. Our code is publicly available and open source, and can also be used to model spatial distributions of other galaxy properties that are traced by its surface brightness profile.

Investigating the scatter origin in CHEX-MATE galaxy cluster X-ray surface brightness profiles

We present the statistical properties and the investigation on the origin of the scatter within the spatially resolved emission measure profiles of the CHEX–MATE sample, formed by 118 galaxy clusters selected via the SZ effect. These objects cover a wide mass, MYSZ500 = [2-15]×1014M⊙, and redshift, z=[0.02, 0.6], range. They have been observed by XMM-Newton with a dedicated program that ensures an unprecedented homogeneous and high quality data. We leveraged this exceptional data set by studying the statistical properties of the surface brightness and emission measure radial profiles. We found that there is a critical scale, R~ 0.4RYSZ500, within which the most morphologically relaxed and disturbed object profiles diverge. Above that radius these differences tend to be within 20%. We complemented the CHEX–MATE clusters with a twin sample drawn from the The Three Hundred suite of cosmological simulations. Leveraging this sample, we were able for the first time to investigate separately the scatter due to projection effects and the one due to cluster-to-cluster differences. We found that projection effects have a smaller impact on the scatter compared to object-to-object differences across all scales. Building on this, we found that below 0.4RYSZ500, the scatter is of the order of 110% reflecting the wide plethora of gas distribution in cluster cores. The scatter is at its minimum, 0.56, in the intermediate range, [0.4-0.8]RYSZ500, despite their morphological status suggesting that clusters are close to the self-similar scenario within this radial range.

The Thickness of Galaxy Disks from z = 5 to 0 Probed by JWST

Although a thick disk is a structure prevalent in local disk galaxies and also present in our home Galaxy, its formation and evolution are still unclear. Whether the thick disk is born thick and/or gradually heated to be thick after formation is under debate. To disentangle these two scenarios, one effective approach is to inspect the thickness of young disk galaxies in the high-redshift Universe. In this work we study the vertical structure of 191 edge-on galaxies spanning redshift from 0.2 to 5 using JWST NIRCAM imaging observations. For each galaxy, we retrieve the vertical surface brightness profile at 1 R e and fit a sech2 function that has been convolved with the line spread function. The obtained scale height of galaxies at z > 1.5 shows no clear dependence on redshift, with a median value in remarkable agreement with that of the Milky Way’s thick disk. This suggests that local thick disks are already thick when they were formed in early times and secular heating is unlikely to be the main driver of thick disk formation. For galaxies at z < 1.5, however, the disk scale height decreases systematically toward lower redshift, with low-redshift galaxies having comparable scale height with that of the Milky Way’s thin disk. This cosmic evolution of disk thickness favors an upside-down formation scenario of galaxy disks.

A multiwavelength study of spiral structure in galaxies. II. Spiral arms in deep optical observations

ABSTRACT In this paper, we look to analyse the spiral features of grand-design, multiarmed, and flocculent spiral galaxies using deep optical imaging from DESI Legacy Imaging Surveys. We explore the resulting distributions of various characteristics of spiral structure beyond the optical radius, such as the distributions of azimuthal angle, the extent of spiral arms, and of the spiral arm widths for the aforementioned galaxy classes. We also compare the measured properties for isolated galaxies and galaxies in groups and clusters. We find that, on average, compared to multiarmed and flocculent spiral galaxies, the spiral arms of grand-design galaxies exhibit slightly larger azimuthal angles, greater extent, and larger widths in the periphery of the galaxy. Furthermore, on average, isolated galaxies tend to have slightly smaller widths of outer spiral arms compared to galaxies in tight environments, which is likely related to the tidally induced mechanism for generating wider outer spiral arms. We also report that breaks of the disc surface brightness profiles are often related to the truncation of spiral arms in galaxies.

3D tomography of the giant Lyα nebulae of z ≈ 3–5 radio-loud AGN

Lyα emission nebulae are ubiquitous around high-redshift galaxies and are tracers of the gaseous environment on scales out to ≳100 pkpc (proper kiloparsec). High-redshift radio galaxies (HzRGs, type-2 radio-loud quasars) host large-scale nebulae observed in the ionised gas differ from those seen in other types of high-redshift quasars. In this work, we exploit MUSE observations of Lyα nebulae around eight HzRGs (2.92 &lt; z &lt; 4.51). All of the HzRGs have large-scale Lyα emission nebulae with seven of them extended over 100 pkpc at the observed surface brightness limit (∼2 − 20 × 10−19 erg s−1 cm−2 arcsec−2). Because the emission line profiles are significantly affected by neutral hydrogen absorbers across the entire nebulae extent, we performed an absorption correction to infer maps of the intrinsic Lyα surface brightness, central velocity, and velocity width, all at the last scattering surface of the observed Lyα photons. We find the following: (i) that the intrinsic surface brightness radial profiles of our sample can be described by an inner exponential profile and a power law in the low luminosity extended part; (ii) our HzRGs have a higher surface brightness and more asymmetric nebulae than both radio-loud and radio-quiet type-1 quasars; (iii) intrinsic nebula kinematics of four HzRGs show evidence of jet-driven outflows but we find no general trends for the whole sample; (iv) a relation between the maximum spatial extent of the Lyα nebula and the projected distance between the active galactic nuclei (AGN) and the centroids of the Lyα nebula; and (v) an alignment between radio jet position angles and the Lyα nebula morphology. All of these findings support a scenario in which the orientation of the AGN has an impact on the observed nebular morphologies and resonant scattering may affect the shape of the surface brightness profiles, nebular kinematics, and relations between the observed Lyα morphologies. Furthermore, we find evidence showing that the outskirts of the ionised gas nebulae may be ‘contaminated’ by Lyα photons from nearby emission halos and that the radio jet affects the morphology and kinematics of the nebulae. Overall, this work provides results that allow us to compare Lyα nebulae around various classes of quasars at and beyond cosmic noon (z ∼ 3).

AGN radiation imprints on the circumgalactic medium of massive galaxies

ABSTRACT Active galactic nuclei (AGNs) in cosmological simulations generate explosive feedback that regulates star formation in massive galaxies, modifying the gas phase structure out to large distances. Here, we explore the direct effects that AGN radiation has on gas heating and cooling within one high-resolution z = 3 dark matter halo as massive as a quasar host (Mh = 1012.5M⊙), run without AGN feedback. We assume AGN radiation to impact the circumgalactic medium (CGM) anisotropically, within a bi-cone of angle α. We find that even a relatively weak AGN (black hole mass M• = 108M⊙ with an Eddington ratio λ = 0.1) can significantly lower the fraction of halo gas that is catastrophically cooling compared to the case of gas photoionized only by the ultraviolet background (UVB). Varying M•, λ, and α, we study their effects on observables. A 109M⊙ AGN with λ = 0.1 and $\alpha \approxeq 60^{^{\rm o}}$ reproduces the average surface brightness (SB) profiles of Ly α, He ii, and C iv, and results in a covering fraction of optically thick absorbers within observational estimates. The simulated SB$_{\rm C\, \rm{\small IV}}$ profile is steeper than observed, indicating that not enough metals are pushed beyond the very inner CGM. For this combination of parameters, the CGM mass catastrophically cooling is reduced by half with respect to the UVB-only case, with roughly same mass out of hydrostatic equilibrium heating up and cooling down, hinting to the importance of self-regulation around AGNs. This study showcases how CGM observations can constrain not only the properties of the CGM itself, but also those of the AGN engine.

Simulations of two-temperature jets in galaxy clusters

Context. Forward shocks by radio jets, driven into the intracluster medium, are one of the indicators that can be used to evaluate the power of the jet. Meanwhile, high-angular-resolution X-ray observations show the Mach numbers of powerful radio jets are smaller compared to the results of theoretical and numerical studies, namely, ℳobs &lt; 2. Aims. Our aim is to systematically investigate various factors, such as projection effects and temperature non-equilibration between protons and electrons, that influence the Mach number estimate in a powerful jet. Methods. Using a two-temperature magnetohydrodynamic simulation data for the Cygnus A radio jets, whose Mach number is approximately 6, we constructed mock X-ray maps of simulated jets from various viewing angles. Furthermore, we evaluated the shock Mach number from the density-temperature jump using the same method of X-ray observations. Results. Our results demonstrate that measurements from the density jump significantly underestimate the Mach numbers, ℳ &lt; 2, around the jet head at a low viewing angle, ⪅50°. The observed post-shock temperature is strongly reduced by the projection effect, as our jet is in the cluster center where the gas density is high. On the other hand, the temperature jump is almost at unity, even if thermal electrons are in instant equilibration with protons. Upon comparison, we find that the shock property of our model at a viewing angle of &lt; 55° is in good agreement with the results of Cygnus A observations. Conclusions. These works illustrate the importance of the projection effect in estimating the Mach number from the surface brightness profile. Furthermore, forward shock Mach numbers could serve as a useful probe for determining viewing angles for young, powerful radio jets.

BASS. XXXIV. A Catalog of the Nuclear Millimeter-wave Continuum Emission Properties of AGNs Constrained on Scales ≤ 100–200 pc

We present a catalog of the millimeter-wave (mm-wave) continuum properties of 98 nearby (z < 0.05) active galactic nuclei (AGNs) selected from the 70 month Swift/BAT hard-X-ray catalog that have precisely determined X-ray spectral properties and subarcsecond-resolution Atacama Large Millimeter/submillimeter Array Band 6 (211–275 GHz) observations as of 2021 April. Due to the hard-X-ray (>10 keV) selection, the sample is nearly unbiased for obscured systems at least up to Compton-thick-level obscuration, and provides the largest number of AGNs with high-physical-resolution mm-wave data (≲100–200 pc). Our catalog reports emission peak coordinates, spectral indices, and peak fluxes and luminosities at 1.3 mm (230 GHz). Additionally, high-resolution mm-wave images are provided. Using the images and creating radial surface brightness profiles of mm-wave emission, we identify emission extending from the central sources and isolated blob-like emission. Flags indicating the presence of these emission features are tabulated. Among 90 AGNs with significant detections of nuclear emission, 37 AGNs (≈41%) appear to have both or one of extended or blob-like components. We, in particular, investigate AGNs that show well-resolved mm-wave components and find that these seem to have a variety of origins (i.e., a jet, radio lobes, a secondary AGN, stellar clusters, a narrow-line region, galaxy disk, active star formation regions, or AGN-driven outflows), and some components have currently unclear origins.

The X-ray invisible Universe. A look into the haloes undetected by eROSITA

ABSTRACT The paper presents the analysis of optically selected GAMA groups and clusters in the SRG/eROSITA X-ray map of eROSITA Final Equatorial Depth Survey, in the halo mass range 1013−5 × 1014 M⊙ and at z &amp;lt; 0.2. All X-ray detections have a clear GAMA counterpart, but most of the GAMA groups in the halo mass range 1013−1014 M⊙ remain undetected. We compare the X-ray surface brightness profiles of the eROSITA detected groups with the mean stacked profile of the undetected low-mass haloes at fixed halo mass. Overall, we find that the undetected groups exhibit less concentrated X-ray surface brightness, dark matter, and galaxy distributions with respect to the X-ray-detected haloes. The mean gas mass fraction profiles are consistent in the two samples within 1.5σ, indicating that the gas follows the dark matter profile. The low-mass concentration and the magnitude gap indicate that these systems are young. They reside with a higher probability in filaments while X-ray-detected groups favour the nodes of the Cosmic Web. Because of the lower central emission, the undetected systems tend to be X-ray underluminous at fixed halo mass and to lie below the LX−Mhalo relation. Interestingly, the X-ray-detected systems inhabiting the nodes scatter the less around the relation, while those in filaments tend to lie below it. We do not observe any strong relationship between the system X-ray appearance and the active galactic nucleus (AGN) activity. We cannot exclude the role of the past AGN feedback in affecting the gas distribution over the halo lifetime. However, the data suggests that the observed differences might be related to the halo assembly bias.

Siena Galaxy Atlas 2020

We present the 2020 version of the Siena Galaxy Atlas (SGA-2020), a multiwavelength optical and infrared imaging atlas of 383,620 nearby galaxies. The SGA-2020 uses optical grz imaging over ≈20,000 deg2 from the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys Data Release 9 and infrared imaging in four bands (spanning 3.4–22 μm) from the 6 year unWISE coadds; it is more than 95% complete for galaxies larger than R(26) ≈ 25″ and r < 18 measured at the 26 mag arcsec−2 isophote in the r band. The atlas delivers precise coordinates, multiwavelength mosaics, azimuthally averaged optical surface-brightness profiles, model images and photometry, and additional ancillary metadata for the full sample. Coupled with existing and forthcoming optical spectroscopy from the DESI, the SGA-2020 will facilitate new detailed studies of the star formation and mass assembly histories of nearby galaxies; enable precise measurements of the local velocity field via the Tully–Fisher and fundamental plane relations; serve as a reference sample of lasting legacy value for time-domain and multimessenger astronomical events; and more.

Outskirts of Abell 1795: Probing gas clumping in the intracluster medium

Contact. The outskirts of galaxy clusters host complex interactions between the intracluster and circumcluster media. During the evolution of clusters, ram-pressure stripped gas clumps from infalling substructures break the uniformity of the gas distribution, potentially leading to observational biases at large radii. However, assessing the contribution of gas clumping poses observational challenges and requires robust X-ray measurements in the background-dominated regime of the cluster outskirts. Aims. The main objectives of this study are to isolate faint gas clumps from field sources and from the diffuse emission in the Abell 1795 galaxy cluster, then to probe their impact on the observed surface brightness and thermodynamic profiles. Methods. We performed an imaging analysis on deep Chandra ACIS-I observations of the Abell 1795 cluster outskirts, extending out to ∼1.5r200 with full azimuthal coverage. We built the 0.7 − 2.0 keV surface brightness distribution from the adaptively binned image of the diffuse emission and looked for clumps in the form of &gt; + 2σ surface brightness outliers. Our classification of the clump candidates was based primarily on Chandra and SDSS data. Benefiting from the point source list resolved by Chandra, we extracted the thermodynamic profiles of the intracluster medium from the associated Suzaku XIS data out to r200 using multiple point source and clump candidate removal approaches. Results. We identified 24 clump candidates in the Abell 1795 field, most of which are likely to be associated with background objects, including active galactic nuclei, galaxies, and clusters or groups of galaxies, as opposed to intrinsic gas clumps. These sources had minimal impact on the surface brightness and thermodynamic profiles of the cluster emission. After correcting for clump candidates, the measured entropy profile still deviates from a pure gravitational collapse, suggesting complex physics at play in the outskirts, which may include potential electron–ion non-equilibrium and non-thermal pressure support.

Morphological Decomposition of the Early-type Spiral Galaxy M81 (NGC 3031)

This paper presents a morphological investigation of the early-type spiral galaxy M81 (NGC 3031) through decomposition by fitting radial profiles of surface brightness using the software GALFIT, aimed at exploring structural components of M81 and quantifying their morphology. In this work, we adopt 6 types of decompositions with different numbers of morphological components, among which the most complicated one contains 5 components such as a bulge, a disk, a pair of outer spiral arms, a pair of inner spiral arms, and a galactic nucleus. The results show that, M81 hosts a classical bulge with the Sérsic index ∼ 5.0; the morphology and the luminosity for the bulge are almost constant in the different decomposition types. The disk of M81 has the Sérsic index ∼ 1.2 but the morphology and the luminosity are found sensitive to the inclusion of the inner spiral arms in the decomposition or not. The results of this work indicate that the combination of individual substructures has a considerable impact on the morphology of the galaxy as a mixture. On the basis of the results, the usability of the different types of decomposition is suggested in this work. The three-component decomposition, i.e., bulge + disk + nucleus, is applicable to statistics of large samples of galaxies; more complicated decomposition with spiral arms taken into account is suitable for precise measurements of individual galaxies in small samples. This work is based on the single-band Spitzer-The Infrared Array Camera (IRAC) 4.5 μm image. In the future, we will carry out multi-wavelength decomposition, for the purpose of investigating spectral energy distributions and stellar population properties for the galactic substructures, and thereby deduce their formation history and evolution processes.

Исследование усреднённых азимутальных профилей поверхностной яркости спиральных рукавов при помощи декомпозиции

For the first time we perform the decomposition of 29 galaxies from S4G survey considering spiral arms as a separate component. We analyze the contribution of spiral arms to the azimuthally-averaged profiles of galaxies’ surface brightness using our models, using models obtained with decomposition. We show that spiral arms’ contribution varies strongly with distance to the center, usually reaching its highest value at the radius of about 1,5 exponential scale of the disk and decreasing to zero at the center and on the periphery of the galaxy. We obtain the characteristic values of the «bump» height on the galaxy’s azimuthally-averaged profile which is caused by the spiral arms. Spiral arms’ contribution to the overall luminosity of the galaxy is investigated, its connection with the Hubble type is also confirmed. Our results can be applied, for the rough estimates of axisymmetric components’ share in galaxy’s light, which is important for determination of disk parameters based on azimuthally-averaged surface brightness profiles, or for analysis of the spectral energy distribution in galaxy.

Much ado about no offset – characterizing the anomalous multiple-image configuration and the model-driven displacement between light and mass in the multiplane strong lens Abell 3827

ABSTRACT Abell 3827 is a unique galaxy cluster with a dry merger in its core causing a highly resolved multiple-image configuration of a blue spiral galaxy at zs = 1.24. The surface brightness profiles of four merging galaxies around zd = 0.099 complicate a clear identification of the number of images and finding corresponding small-scale features across them. The entailed controversies about offsets between luminous and dark matter have never been settled and dark matter characteristics in tension with bounds from complementary probes and simulations seemed necessary to explain this multiple-image configuration. We resolve these issues with a systematic study of possible feature matchings across all images and their impact on the reconstructed mass density distribution. From the local lens properties directly constrained by these feature matchings without imposing any global lens model, we conclude that none of them are consistent with expected local characteristics from standard single-lens-plane lensing, nor can they be motivated by the light distribution in the cluster. Inspecting complementary spectroscopic data, we show that all these results originate from an insufficient constraining power of the data and seem to hint at a thick lens and not at exotic forms of dark matter or modified gravity. If the thick-lens hypothesis can be corroborated with follow-up multiplane lens modelling, A3827 suffers from a full three-dimensional degeneracy in the distribution of dark matter because combinations of shearings and scalings in a single lens plane can also be represented by an effective shearing and a rotation caused by multiple lens planes.