Structure and evolution of simulated dwarf galaxies and Milky Way satellites in Cold and Warm dark matter models

The satellite galaxies and dwarf galaxies in the neighborhood of the Milky Way provide us with detailed observations that can be used to test our standard model of cosmology and structure formation, the $\Lambda$CDM model. I present a sample of 27 cosmological hydrodynamical simulations with virial masses between $5\times 10^8$ and 10^{10}\,\Msun that are aimed to study the properties of dwarf galaxies before accretion. The simulated galaxies are able to reproduce observed scaling relations like the dispersion - size and metallicity - stellar mass relation. The stochasticity of merger induced star formation causes a large scatter in the stellar mass - halo mass relation. In galaxies of stellar masses below 10^6 \, \Msun stellar feedback is unable to affect the dark matter halo and hence those galaxies retain a cuspy profile. A subsample of 7 halos is used as initial conditions for simulations of satellite - host galaxy interactions in a Milky Way mass halo. The mass removal due to tidal forces creates flat stellar velocity dispersion profiles and efficiently decreases the circular velocity at $0.5\,\mathrm{kpc}$ without stripping a large amount of stars. Additionally the stripping seems to happen in a way that effectively steepens the central dark matter density slope. To investigate the effects of warm dark matter on dwarf galaxies and Milky Way satellites I repeat the study in a $3\,\mathrm{keV}$ warm dark matter scenario. I present the simulations of 21 halos in both CDM and WDM. In WDM the critical halo mass for the onset of star formation is shifted towards higher masses, while the simulations that do produce stars, reproduce the same scaling relations as their CDM counterparts. However, WDM seems to delay the bulk star formation, making galaxies in CDM look about $2\,\mathrm{Gyr}$ older. While halo concentrations are significantly lower in WDM, the central dark matter density slope is slightly steeper for the low mass end. For four halos (in WDM and CDM) I present their evolution as Milky Way satellites. In contrast to the CDM halos, WDM halos are stripped more effective due to their lower concentrations. The survival probability for WDM satellites, on the other hand, is not necessarily lower because of their steeper central slope. Again, the WDM as well as CDM satellites end up with very cuspy profiles after being stripped. I come to the conclusion that the predictions from my simulations do not challenge the $\Lambda$CDM compared to current observational data of dwarf galaxies and Milky Way satellites. An observation of a cored density profile in one of the very low mass objects, however, would force us reconsider the dark matter model. Also WDM would not pose a solution to this problem

The edge of galaxy formation III: The effects of warm dark matter on Milky Way satellites and field dwarfs

In this third paper of the series, we investigate the effects of warm dark matter with a particle mass of $m_\mathrm{WDM}=3\,\mathrm{keV}$ on the smallest galaxies in our Universe. We present a sample of 21 hydrodynamical cosmological simulations of dwarf galaxies and 20 simulations of satellite-host galaxy interaction that we performed both in a Cold Dark Matter (CDM) and Warm Dark Matter (WDM) scenario. In the WDM simulations, we observe a higher critical mass for the onset of star formation. Structure growth is delayed in WDM, as a result WDM haloes have a stellar population on average two Gyrs younger than their CDM counterparts. Nevertheless, despite this delayed star formation, CDM and WDM galaxies are both able to reproduce the observed scaling relations for velocity dispersion, stellar mass, size, and metallicity at $z=0$. WDM satellite haloes in a Milky Way mass host are more susceptible to tidal stripping due to their lower concentrations, but their galaxies can even survive longer than the CDM counterparts if they live in a dark matter halo with a steeper central slope. In agreement with our previous CDM satellite study we observe a steepening of the WDM satellites' central dark matter density slope due to stripping. The difference in the average stellar age for satellite galaxies, between CDM and WDM, could be used in the future for disentangling these two models.Comment: 10 pages, 11 figures, accepted for publication on MNRA

Stroma-regulated HMGA2 is an independent prognostic marker in PDAC and AAC

Background: The HMGA2 protein has experimentally been linked to EMT and cancer stemness. Recent studies imply that tumour-stroma interactions regulate these features and thereby contribute to tumour aggressiveness. Methods: We analysed 253 cases of pancreatic ductal adenocarcinoma (PDAC) and 155 cases of ampullary adenocarcinoma (AAC) for HMGA2 expression by IHC. The data were correlated with stroma abundance and supplemented by experimental studies. Results: HMGA2 acts as an independent prognostic marker associated with a significantly shorter overall survival in both tumour types. Overall, HMGA2-positivity was more frequent in patients with PDAC than with AAC. The HMGA2 status in tumour cells significantly correlated with the abundance of PDGFRβ-defined stroma cells. In vivo co-injection of Panc-1 cancer cells with pancreatic stellate cells increased tumour growth in a manner associated with increased HMGA2 expression. Furthermore, in vitro treatment of Panc-1 with conditioned media from PDGF-BB-activated stellate cells increased their ability to form tumour spheroids. Conclusions: This study identifies HMGA2 expression in tumour cells as an independent prognostic marker in PDAC and AAC. Correlative data analysis gives novel tissue-based evidence for a heterotypic cross-talk with stroma cells as a possible mechanism for HMGA2 induction, which is further supported by experimental models

Dual-Phase PET-CT to Differentiate [F-18]Fluoromethylcholine Uptake in Reactive and Malignant Lymph Nodes in Patients with Prostate Cancer

PURPOSE: To investigate whether time-trends of enhanced [(18)F]Fluoromethylcholine ([(18)F]FCH) in lymph nodes (LN) of prostate cancer (PCa) patients can help to discriminate reactive from malignant ones, and whether single time point standardized uptake value (SUV) measurements also suffice. PROCEDURES: 25 PCa patients with inguinal (presumed benign) and enlarged pelvic LN (presumed malignant) showing enhanced [(18)F]FCH uptake at dual-phase PET-CT were analyzed. Associations between LN status (benign versus malignant) and SUV(max) and SUV(meanA50), determined at 2 min (early) and 30 min (late) post injection, were assessed. We considered two time-trends of [(18)F]FCH uptake: type A (SUV early > SUV late) and type B (SUV late ≥ SUV early). Histopathology and/or follow-up were used to confirm the assumption that LN with type A pattern are benign, and LN with type B pattern malignant. RESULTS: Analysis of 54 nodes showed that LN status, time-trends, and 'late' (30 min p.i.) SUV(max) and SUV(meanA50) parameters were strongly associated (P<0.0001). SUV(max) relative difference was the best LN status predictor. All but one inguinal LN showed a decreasing [(18)F]FCH uptake over time (pattern A), while 95% of the pelvic nodes presented a stable or increasing uptake (pattern B) type. CONCLUSIONS: Time-trends of enhanced [(18)F]FCH uptake can help to characterize lymph nodes in prostate cancer patients. Single time-point SUV measurements, 30 min p.i., may be a reasonable alternative for predicting benign versus malignant status of lymph nodes, but this remains to be validated in non-enlarged pelvic lymph nodes

The edge of galaxy formation – I. Formation and evolution of MW-satellite analogues before accretion

International audienc

The edge of galaxy formation – II. Evolution of Milky Way satellite analogues after infall

International audienc