Your search for "Fornax Dwarf Galaxy" returned 436 results

We have measured the absolute proper motion of the Fornax dwarf spheroidal galaxy from a combination of photographic plate material and Hubble Space Telescope Wide Field Planetary Camera 2 data that provide a time baseline of up to 50 yr. The extragalactic reference frame consists of eight QSO images and 48 galaxies. The absolute proper motion is μ_α cos δ = 0.59 ± 0.16 mas yr^-1 and μ_δ = -0.15 ± 0.16 mas yr^-1. The corresponding orbit of Fornax is polar, with an eccentricity of 0.27 and a radial period of 4.5 Gyr. Fornax's current location is near pericenter. The direction of the motion of Fornax supports the notion that Fornax belongs to the Fornax–Leo I–Leo II–Sculptor–Sextans stream as hypothesized by both Lynden-Bell and Majewski. According to our orbit determination, Fornax crossed the Magellanic plane ∼190 Myr ago, a time that coincides with the termination of the star formation process in Fornax. We propose that ram pressure stripping due to the passage of Fornax through a gaseous medium denser than the typical intragalactic medium left behind from the LMC may have caused the end of star formation in Fornax. The excess, anomalous clouds within the south Galactic pole region of the Magellanic Stream, whose origin has long been debated in the literature as constituents of either the Magellanic Stream or of the extragalactic Sculptor group, are found to lie along the orbit of Fornax. We speculate that these clouds are stripped material from Fornax as the dwarf crossed the orbit of the Magellanic Clouds.

We report the discovery of 271 previously undetected dwarf galaxies in the outer Fornax cluster regions at radii r_vir/4 < r < r_vir/2 using data from the Next Generation Fornax Survey (NGFS) with deep coadded u', g', and i' images obtained with Blanco/DECam at Cerro Tololo Interamerican Observatory. From the 271 dwarf candidates, we find 39 to be nucleated. Together with our previous study of the central Fornax region, the new dwarfs detected with NGFS data number 392, of which 56 are nucleated. The total Fornax dwarf galaxy population from NGFS and other catalogs rises, therefore, to a total of 643 with 181 being nucleated, yielding an overall nucleation fraction of 28%. The absolute i'-band magnitudes for the outer NGFS dwarfs are in the range −18.80 ≤  M_i' ≤  −8.78 with effective radii r_eff,i' = 0.18–2.22 kpc and an average Sérsic index $\langle n{\rangle }_{i^{\prime} }\,=0.81$. Nonnucleated dwarfs are found to be fainter and smaller by ${\rm{\Delta }}\langle {M}_{i^{\prime} }\rangle =2.25$ mag and ${\rm{\Delta }}\langle {r}_{\mathrm{eff},i^{\prime} }\rangle =0.4\,\mathrm{kpc}$ than the nucleated dwarfs. We demonstrate a significant clustering of dwarf galaxies on scales ≲100 kpc, and projected surface number density profile estimates, Σ_N(r), show a concentration of dwarfs in the Fornax core region within r ≲ 350 kpc. Σ_N(r) has a flat distribution up to ∼350 kpc, beyond which it declines for the nonnucleated dwarfs. The nucleated dwarfs have a steeper Σ_N(r) distribution, are more concentrated toward NGC 1399, and are decreasing rapidly outwards. This is the first time the transition from cluster to field environment has been established for the very faint dwarf galaxy population with robust sample statistics.

The Fornax dwarf spheroidal galaxy has an anomalous number of globular clusters, five, for its stellar mass. There is a longstanding debate about a potential sixth globular cluster (Fornax 6) that has recently been "rediscovered" in DECam imaging. We present new Magellan/M2FS spectroscopy of the Fornax 6 cluster and Fornax dSph. Combined with literature data we identify ∼15–17 members of the Fornax 6 cluster, showing that this overdensity is indeed a star cluster and associated with the Fornax dSph. The cluster is significantly more metal-rich (mean metallicity of $\overline{[\mathrm{Fe}/{\rm{H}}]}$ = −0.71 ± 0.05) than the other five Fornax globular clusters (−2.5 < [Fe/H] < −1.4) and more metal-rich than the bulk of Fornax. We measure a velocity dispersion of ${5.6}_{-1.6}^{+2.0}\mathrm{km}\,{{\rm{s}}}^{-1}$ corresponding to an anomalously high mass-to-light of 15 < M/L < 258 at 90% confidence when calculated assuming equilibrium. Two stars inflate this dispersion and may be either Fornax field stars or as yet unresolved binary stars. Alternatively, the Fornax 6 cluster may be undergoing tidal disruption. Based on its metal-rich nature, the Fornax 6 cluster is likely younger than the other Fornax clusters, with an estimated age of ∼2 Gyr when compared to stellar isochrones. The chemodynamics and star formation history of Fornax shows imprints of major events such as infall into the Milky Way, multiple pericenter passages, star formation bursts, and/or potential mergers or interactions. Any of these events may have triggered the formation of the Fornax 6 cluster.

It has been well established that dwarf early-type galaxies (ETGs) can often exhibit a complex morphology, whereby faint spiral arms, bars, edge-on disks, or clumps are embedded in their main, brighter diffuse body. In our first paper ("Brought to Light I"), we developed a new method for robustly identifying and extracting substructures in deep imaging data of dwarf ETGs in the Virgo galaxy cluster. Here we apply our method to a sample of 23 dwarf ETGs in the Fornax galaxy cluster, out of which 9 have disk-like and 14 have clump-like substructures. According to Fornax Deep Survey (FDS) data, our sample constitutes 12% of all dwarf ETGs in Fornax brighter than M_r = − 13 mag, and contains all cases that unequivocally exhibit substructure features. We use g- and r-band FDS images to measure the relative contribution of the substructures to the total galaxy light and to estimate their g − r colors. We find that the substructures typically contribute 8.7% and 5.3% of the total galaxy light in the g and r bands, respectively, within two effective radii. Disk substructures are usually found in dwarf ETGs with redder global colors, and they can be either as red as or bluer than their galaxy's diffuse component. In contrast, the clump substructures are found in comparatively bluer dwarf ETGs, and they are always bluer than their galaxy's diffuse component. These results provide further evidence that dwarf ETGs can hide diverse complex substructures, with stellar populations that can greatly differ from those of the dominant diffuse light in which they are embedded.

Near-infrared spectra were obtained for 117 red giants in the Fornax dwarf spheroidal galaxy with the FORS1 spectrograph on the VLT, in order to study the metallicity distribution of the stars and to lift the age-metallicity degeneracy of the red giant branch (RGB) in the color-magnitude diagram (CMD). Metallicities are derived from the equivalent widths of the infrared calcium triplet lines at 8498, 8542, and 8662 Å, calibrated with data from globular clusters, the open cluster M67, and the LMC. For a substantial portion of the sample, the strength of the calcium triplet is unexpectedly high, clearly indicating that the main stellar population of Fornax is significantly more metal-rich than could be inferred from the position of its RGB in the CMD. We show that the relative narrowness of the RGB in Fornax is caused by the superposition of stars of very different ages and metallicities. The region of parameter space occupied by the most metal-rich red giants in Fornax—young, metal-rich, and luminous—is not covered by any of the calibrating clusters, which introduces uncertainty in the high end of the metallicity scale. Using published theoretical calculations of Ca II triplet equivalent widths, we have investigated their sensitivity to luminosity, age, and metallicity. The correlation between absolute I magnitude and Ca II strength appears to be only slightly affected by age variations, and we have used it to estimate the metallicities of the Fornax stars. The metallicity distribution in Fornax is centered at [Fe/H] = -0.9, with a metal-poor tail extending to [Fe/H] ≃ -2. While the distribution to higher metallicities is less well determined by our observations, the comparison with LMC data indicates that it extends to [Fe/H] ∼ -0.4. By comparing the metallicities of the stars with their positions in the CMD, we have derived the complex age-metallicity relation of Fornax. In the first few gigayears, the metal abundance rose to [Fe/H] ∼ -1.0 dex. The enrichment accelerated in the past ∼1–4 Gyr to reach [Fe/H] ∼ -0.4 dex. More than half the sample is constituted of stars younger than ∼4 Gyr, thus indicating sustained recent star formation in Fornax. These results are briefly compared with the theoretical predictions on the evolution of dwarf galaxies. They indicate that the capacity of dwarf spheroidal galaxies to retain the heavy elements that they produce is larger than expected.

The results of a photometric survey of the Fornax dwarf spheroidal galaxy are presented herein. Accurate photometry in two colors (V and I) was collected over a 10 deg² area centered on the Fornax system with the aim of searching for extratidal structure. The data were complete to a magnitude of V = 20, or approximately 1 mag brighter than the Fornax red clump stars. Stars were selected with a color and magnitude lying near the Fornax red giant branch, thereby reducing contamination from the field-star population. We were thus able to probe the outer structure of this dwarf galaxy. Immediately visible was a shell-like structure located 13 northwest from the center of Fornax, approximately 30' beyond the nominal tidal radius at this position angle. We have measured the absolute visual magnitude of this feature to be M_V ∼ -7. The feature is aligned with a previously reported shell (age ∼ 2 Gyr) located near the core radius of Fornax. A statistical analysis of the extratidal stellar distribution further revealed two lobes situated on the Fornax minor axis that are aligned with the two shell-like features. The two-lobed structure combined with the two shells provide strong evidence that Fornax has experienced a merger event in the relatively recent past.

Using deep wide-field photometry 3 yr data (Y3) from the Dark Energy Survey (DES), we present a panoramic study of the Fornax dwarf spheroidal galaxy. The data presented here—a small subset of the full survey—uniformly cover a region of 25 deg² centered on the galaxy to a depth of g ∼ 23.5. We use these data to study the structural properties of Fornax, overall stellar population, and its member stars in different evolutionary phases. We also search for possible signs of tidal disturbance. Fornax is found to be significantly more spatially extended than what early studies suggested. No statistically significant distortions or signs of tidal disturbances were found down to a surface brightness limit of ∼32.1 mag arcsec⁻². However, there are hints of shell-like features located ∼20'–40' from the center of Fornax that may be stellar debris from past merger events. We also find that intermediate-age and young main-sequence populations show different orientation at the galaxy center and have many substructures. The deep DES Y3 data allow us to characterize the age of those young stellar substructures with great accuracy, both those previously known and those newly identified as possible overdensities in this work, on the basis of their color–magnitude diagram morphology. We find that the youngest overdensities are all found on the eastern side of Fornax, where the Fornax field population itself is slightly younger than in the west. In summary, the high-quality DES Y3 data reveal that Fornax has many rich structures and provide insights into its complex formation history.

I determine a distance to the Fornax dwarf galaxy using stars in the red clump and at the tip of the red giant branch. They are in very good agreement, with μ₀ = 20.66 mag. Comparing the magnitudes of the tip of the red giant branch and of the red clump in Fornax, Carina, and the Magellanic Clouds, I propose a possible solution to the problem of the discrepancy between these two types of distance measurements.

We present a search for variable stars in the Fornax dwarf galaxy covering an area of half a square degree. We have ∼30 epochs of VI data. We found and determined periods for more than 500 RR Lyrae, 17 anomalous Cepheids, and six Population II Cepheids. In addition we have 85 candidate long-period variables, the majority of which were previously unknown. We estimate that the average metal abundance of RR Lyrae stars is [Fe/H] ≃ -1.6 dex.