ABSTRACT
We present a photometric study of the dwarf galaxy population in the low to moderate density environments of the MATLAS (Mass Assembly of early-Type gaLAxies with their fine Structures) deep ...imaging survey. The sample consists of 2210 dwarfs, including 508 nucleated. We define a nucleus as a compact source that is close to the galaxy photocentre (within 0.5 $R_\mathrm{ e}$) which is also the brightest such source within the galaxy’s effective radius. The morphological analysis is performed using a 2D surface brightness profile modelling on the g-band images of both the galaxies and nuclei. Our study reveals that, for similar luminosities, the MATLAS dwarfs show ranges in the distribution of structural properties comparable to cluster (Virgo and Fornax) dwarfs and a range of sizes comparable to the Local Group and Local Volume dwarfs. Colour measurements using the r- and i-band images indicate that the dwarfs in low and moderate density environments are as red as cluster dwarfs on average. The observed similarities between dwarf ellipticals in vastly different environments imply that dEs are not uniquely the product of morphological transformation due to ram-pressure stripping and galaxy harassment in high density environments. We measure that the dwarf nuclei are located predominantly in massive, bright and round dwarfs and observe fewer nuclei in dwarfs with a faint centre and a small size. The colour of the galaxy nucleus shows no clear relation to the colour of the dwarf, in agreement with the migration and wet migration nucleus formation scenarios. The catalogues of the MATLAS dwarfs photometric and structural properties are provided.
Stellar shells around galaxies could provide precious insights into their assembly history. However, their formation mechanism remains poorly empirically constrained, regarding in particular the type ...of galaxy collisions at their origin. We present MUSE at VLT data of the most prominent outer shell of NGC 474, to constrain its formation history. The stellar shell spectrum is clearly detected, with a signal-to-noise ratio of ∼65 pix
−1
. We used a full spectral fitting method to determine the line-of-sight velocity and the age and metallicity of the shell and associated point-like sources within the MUSE field of view. We detect six globular cluster (GC) candidates and eight planetary nebula (PN) candidates that are all kinematically associated with the stellar shell. We show that the shell has an intermediate metallicity, M/H = −0.83
−0.12
+0.12
, and a possible
α
-enrichment,
α
/Fe ∼ 0.3. Assuming the material of the shell comes from a lower mass companion, and that the latter had no initial metallicity gradient, such a stellar metallicity would constrain the mass of the progenitor at around 7.4 × 10
8
M
⊙
, implying a merger mass ratio of about 1:100. However, our census of PNe and earlier photometry of the shell would suggest a much higher ratio, around 1:20. Given the uncertainties, this difference is only significant at the ≃1
σ
level. We discuss the characteristics of the progenitor, and in particular whether the progenitor could also be composed of stars from the low-metallicity outskirts of a more massive galaxy. Ultimately, the presented data do not allow us to put a firm constraint on the progenitor mass. We show that at least two GC candidates possibly associated with the shell are quite young, with ages below 1.5 Gyr. We also note the presence of a young (∼1 Gyr) stellar population in the center of NGC 474. The two may have resulted from the same event.
The blind H
I
survey Arecibo Galaxy Environment Survey (AGES) detected several unresolved sources in the Virgo cluster, which do not have optical counterparts in the Sloan Digital Sky Survey. The ...origin of these dark clouds is unknown. They might be crucial objects since they could be the so-called dark galaxies, that is, the dark matter halos without stellar content that are expected from cosmological simulations. In order to reveal the nature of the dark clouds, we took a deep optical image of one them, AGESVC1 282, with the newly-commissioned 1.4 m
Milanković
Telescope. After observing it for 10.4 h in the
L
-filter, the image reached a surface-brightness limit of about 29.1 mag arcsec
−2
in
V
. No optical counterpart was detected. We placed an upper limit on the
V
-band luminosity of the object of 1.1 × 10
7
L
⊙
, giving a stellar mass below 1.4 × 10
7
M
⊙
and a H
I
-to-stellar mass ratio above 3.1. By inspecting archival H
I
observations of the surrounding region, we found that none of the standard explanations for optically dark H
I
clouds fits the available constraints on this object.
The presence of HI gas in galaxies is inextricably linked to their morphology and evolution. This paper aims to understand the HI content of the already identified 2210 dwarfs located in the ...low-to-moderate density environments of the Mass Assembly of early-Type GaLAxies with their fine Structures (MATLAS) deep imaging survey. We combined the HI observations from the ATLAS
3D
survey, with the extragalactic HI sources from the Arecibo Legacy Fast ALFA survey, to extract the HI line width, velocity, and mass of the MATLAS dwarfs. From the 1773 dwarfs in our sample with available HI observations, 8% (145) have an HI line detection. The majority of the dwarfs show an irregular morphology, while 29% (42) are ellipticals, which is the largest sample of HI-bearing dwarf ellipticals (dEs) to date. Of the HI dwarf sample, 2% (three) are ultra-diffuse galaxies (UDGs), 12% have a transition-type morphology, 5% are tidal dwarf candidates, and 10% appear to be disrupted objects. In our optically selected sample, 9.5% of the dEs, 7% of the UDGs, and 10% of the classical dwarfs are HI-bearing. The HI-bearing dwarfs have, on average, bluer colors than the dwarfs without detected HI. We find relations between the stellar and HI masses, gas fraction, color, and absolute magnitude to be consistent with previous studies of dwarfs probing similar masses and environments. For 79% of the dwarfs identified as satellites of massive early-type galaxies, we find that the HI mass increases with the projected distance to the host. Using the HI line width, we estimate dynamical masses and find that 5% (seven) of the dwarfs are dark matter deficient.
Context.
A small fraction of early-type galaxies (ETGs) show prolate rotation; that is, they rotate around their long photometric axis. In simulations, certain configurations of galaxy mergers are ...known to produce this type of rotation.
Aims.
We investigate the association of prolate rotation and signs of galaxy interactions among the observed galaxies.
Methods.
We collected a sample of 19 nearby ETGs with distinct prolate rotation from the literature and inspected their ground-based deep optical images for interaction signs – 18 in archival images and 1 in a new image obtained with the Milanković telescope.
Results.
Tidal tails, shells, disturbed asymmetric stellar halos, or ongoing interactions are present in all the 19 prolate rotators. Comparing this with the frequency of tidal disturbance among the general sample of ETGs of a roughly similar mass range and surface-brightness limit, we estimate that the chance probability of such an observation is only 0.00087. We also find a significant overabundance of prolate rotators that are hosting multiple stellar shells. The visible tidal features imply a relatively recent galaxy interaction. That agrees with the Illustris large-scale cosmological hydrodynamical simulation, where prolate rotators are predominantly formed in major mergers during the last 6 Gyr. In the appendix, we present the properties of an additional galaxy, NGC 7052, a prolate rotator for which no deep images are available, but for which an HST image revealed the presence of a prominent shell, which had not been reported before.
The possible existence of two dark-matter-free galaxies (NGC 1052-DF2 and NGC 1052-DF4) in the field of the early-type galaxy NGC 1052 presents a challenge to theories of dwarf galaxy formation ...according to the current cosmological paradigm. We carried out a search for signatures of past interactions connected to the putative hosts of NGC 1052-DF2 and NGC 1052-DF4 using a very deep L-band image obtained with the 0.7 m Jeanne Rich telescope that reach a surface brightness limit of 28.5 mag arcsec−2 in the r band. We found several low-surface brightness features, possibly consistent with an ongoing merger history in this group. We find a tidal interaction between NGC 1052 and NGC 1047, confirming a physical association. Furthermore, we find a stellar loop around NGC 1052 in the direction of NGC 1042 and a stellar stream pointing in the direction of NGC 1052-DF2, but they are not directly connected. We find no evidence for a recent tidal interaction for NGC 1052-DF2 and NGC 1052-DF4. No LSB features have been uncovered around the spiral galaxy NGC 1042, which leaves the association (physical or projected) between NGC 1052 and NGC 1042 ambiguous, although they have similar radial velocities. Their association will only be established when accurate distances to both objects have been measured.
Context.
The lenticular galaxy NGC 474 hosts a rich system of tidal shells and streams, some of which are exceptionally bright. Two teams recently presented spectroscopic observations of the ...brightest shells. These were the first shell spectra ever observed in integrated starlight. The authors studied the stellar populations of the shell, of the center of the galaxy, and of its globular clusters. The precise formation scenario for the tidal features of this prominent galaxy still remained unclear, however.
Aims.
Here, we add further clues on their formation from the radii of the shells, and we present a scenario for the formation of the tidal features that seems to be unique and can explain all available data.
Methods.
Shell radii were analyzed with the shell identification method, and we ran self-consistent simulations of the formation of the tidal features. We considered Newtonian as well as MOND gravity.
Results.
Observations suggest that the tidal features originate from the accretion of a spiral galaxy. According to the shell identification method, the merging galaxies first collided 1.3 Gyr ago and then again 0.9 Gyr ago, thereby forming the shells in two generations. This would also explain the young ages of stellar populations in the center of the galaxy and the young age of the globular clusters. The analytic models of shell propagation that underlie the shell identification method are verified by a simulation. The simulations reproduce the observed morphology of the tidal features well. The accreted spiral likely reached NGC 474 on the plane of the sky nearly radially from the south, its rotation axis pointing toward us. It probably had a stellar mass of about one-sixth of NGC 474, that is, 10
9.8
M
⊙
. Apparently, all tidal features in the galaxy originate from one merger.
We report that the density profiles of globular cluster (GC) systems in a sample of 17 early-type galaxies (ETGs) show breaks at the radii where the gravitational acceleration exerted by the stars ...equals the galactic acceleration scale a0 known from the radial acceleration relation or the modified Newtonian dynamics (MOND). The match with the other characteristic radii in the galaxy is not that close. We propose possible explanations in the frameworks of the Lambda cold dark matter (ΛCDM) model and MOND. We find tentative evidence that in the ΛCDM context, GCs reveal not only the masses of the dark halos through the richness of the GC systems but also the concentrations through the break radii of the GC systems.
Bifunctional ketiminate zinc complexes were synthesized via alkyl or LiCl elimination route from appropriate zinc species (ZnCl2 or ZnEt2) and methoxyaryl substituted monoanionic ketimine {2- or 3- ...or 4-(MeO)C6H4}N(H)C(Me)=CHC(Me)=O. Homo- or heteroleptic complexes were prepared and characterized by the help of multinuclear NMR spectroscopy techniques. One of the heteroleptic ethyl substituted zinc complexes - {κ2-N,O-(2-MeO)C6H4NC(Me)–CHC(Me)–OZnEt}2 was selected for further reactivity experiments with alcohols and amines. Molecular structures of some products were determined by X-Ray diffraction methods showing di- or trinuclear arrangement in solid state caused by the presence of intramolecular zinc–oxygen or zinc–nitrogen bridges. {κ2-N,O-(2-MeO)C6H4NC(Me)–CHC(Me)–OZnEt}2 was also screened for of its catalytic activity in co/polymerization reactions (ROP: trimethylene carbonate, ɛ-caprolactone, l-lactide; copolymerization of epoxides with CO2).
Homo- and heteroleptic zinc complexes containing monoanionic methoxyaryl substituted ketiminate ligands were synthesized and characterized. Selected complex was studied for further reactivity with alcohols and amines and also screened as co-initiator of various co/polymerization reactions. Display omitted
•Homo- and heteroleptic zinc complexes were prepared.•Monoanionic potentially terdenate ketiminate ligands were used.•Reactivity studies of heteroleptic ethyl zinc complex with alcohols and amines was performed.•Heteroleptic ethyl zinc complex was screened in as a catalyst in various co/polymerization reactions.
If modified gravity holds, but the weak lensing analysis is done in the standard way, one finds that dark matter halos have peculiar shapes, not following the standard Navarro-Frenk-White profiles, ...and are fully predictable from the distribution of baryons. Here we study in detail the distribution of the apparent dark matter around point masses, which approximate galaxies and galaxy clusters, and their pairs for the QUMOND MOND gravity, taking an external gravitational acceleration \(g_e\) into account. At large radii, the apparent halo of a point mass \(M\) is shifted against the direction of the external field. When averaged over all lines-of-sight, the halo has a hollow center, and denoting the by \(a_0\) the MOND acceleration constant, its density behaves like \(\rho(r)=\sqrt{Ma_0/G}/(4\pi r^2)\) between the galacticentric radii \(\sqrt{GM/a_0}\) and \(\sqrt{GMa_0}/g_e\), and like \(\rho\propto r^{-7}G^2M^3a_0^3/g_e^5\) further away. Between a pair of point masses, there is a region of a negative apparent dark matter density, whose mass can exceed the baryonic mass of the system. The density of the combined dark matter halo is not a sum of the densities of the halos of the individual points. The density has a singularity near the zero-acceleration point, but remains finite in projection. We compute maps of the surface density and the lensing shear for several configurations of the problem, and derive formulas to scale them to further configurations. In general, for a large subset of MOND theories in their weak field regime, for any configuration of the baryonic mass \(M\) with the characteristic size of \(d\), the total lensing density scales as \(\rho({\vec{x}})=\sqrt{Ma_0/G}d^{-2}f\left(\vec{\alpha},\vec{x}/d,g_ed/\sqrt{GMa_0}\right)\), where the vector \(\vec{\alpha}\) describes the geometry of the system. Distinguishing between QUMOND and cold dark matter seems possible with the existing instruments.
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