Astrophysics - Galactic Profiles and Measurements
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Questions and Answers

What does the Sersic profile model primarily represent?

  • Spiral arms of galaxies
  • Intergalactic medium
  • Dark matter concentration
  • Elliptical galaxies and bulges (correct)

Type I profiles follow a double exponential law.

False (B)

What is the central intensity in the exponential function represented as?

I0

The transition of the electron spin in hydrogen atoms is responsible for the ______ line.

<p>21 cm Hydrogen</p> Signup and view all the answers

Which of the following is a characteristic of Type II profiles?

<p>Double exponential law with a break radius (C)</p> Signup and view all the answers

CO is the most abundant molecule in molecular clouds after H2.

<p>True (A)</p> Signup and view all the answers

What is the parameter 'bn' in the Sersic profile used for?

<p>Ensures that re contains half the light</p> Signup and view all the answers

Match the following disk profile types with their descriptions:

<p>Type I = Single exponential profile Type II = Double exponential with a break radius Type III = Up-bending in outer parts</p> Signup and view all the answers

What is the estimated number of stars in the Milky Way?

<p>100 billion (C)</p> Signup and view all the answers

The Dark Matter Halo of the Milky Way has a mass of approximately $10^{12} M_{igodot}$.

<p>True (A)</p> Signup and view all the answers

What is the Hubble constant according to the 2018 Planck observations?

<p>67.66 ± 0.42 km/s/Mpc</p> Signup and view all the answers

The typical speed of stars in a circular orbit in the Milky Way is approximately __________ km/s.

<p>200</p> Signup and view all the answers

Match the following galaxies with their distances from Earth:

<p>Sagittarius dwarf = 24 kpc Large Magellanic Cloud = 45-50 kpc Andromeda Galaxy = 780 kpc Virgo Cluster = 17 Mpc</p> Signup and view all the answers

What percentage of the total mass of the Milky Way is made up of dark matter?

<p>85.8% (C)</p> Signup and view all the answers

Photometry measures the intensity of radiation from astronomical objects across all wavelengths.

<p>False (B)</p> Signup and view all the answers

What is the diameter range of galaxy clusters as mentioned in the context?

<p>1 - 5 kpc</p> Signup and view all the answers

What is the unit of luminosity measured in astronomical objects?

<p>[erg/s] (D)</p> Signup and view all the answers

The flux F of an astronomical source is independent of its distance D.

<p>False (B)</p> Signup and view all the answers

What is the formula for calculating bolometric luminosity (Lbol)?

<p>Lbol = ∫ Lλ dλ</p> Signup and view all the answers

The apparent magnitude m is calculated using the formula m = m0 − 2.5 log(F), where m0 corresponds to what value for F0?

<p>3631 [Jy]</p> Signup and view all the answers

Match the following galaxy classification methods with their descriptions:

<p>Hubble sequence = Visual classification based on light concentration CAS classification = Model independent classification Photometric decomposition = Model dependent classification</p> Signup and view all the answers

Which of the following is NOT a characteristic used in the Hubble classification?

<p>Color of the galaxy (C)</p> Signup and view all the answers

Vega is assumed to have a magnitude of 0 for all wavelengths (mλ = 0).

<p>True (A)</p> Signup and view all the answers

What is the significance of Jansky units in measuring intensity or surface brightness?

<p>1 [Jy] = 10−23 [erg/s/cm2/Hz]</p> Signup and view all the answers

What is one benefit of using Hα emissions in observations?

<p>It provides good spatial resolution and is a very bright line. (D)</p> Signup and view all the answers

H I has better angular resolution than Hα.

<p>False (B)</p> Signup and view all the answers

What causes the formation of H+ clouds in HII regions?

<p>Photoionization of neutral H by UV photons emitted by young stars.</p> Signup and view all the answers

The systemic velocity along the line of sight is represented as _____ = v(0) = vcosm + vpec,gal + vpec,M W + v⊙ + v⊕ + v⊕,rot.

<p>vsys</p> Signup and view all the answers

Match the following observational techniques with their characteristics:

<p>Absorption stellar lines = Traces stellar movements and needs high S/N spectra Long-slit spectroscopy = Combines 2D image and spectrum of a region H I observations = Less sensitive observations due to dense cloud presence Datacubes = Reconstructed 2D image from spectral data</p> Signup and view all the answers

What is one problem associated with Hα emissions?

<p>Patchy emission and incomplete coverage in separate galactic parts. (D)</p> Signup and view all the answers

The Doppler effect is used to derive the velocities in galaxies.

<p>True (A)</p> Signup and view all the answers

Cold dense clouds are primarily composed of _____ molecules.

<p>H2</p> Signup and view all the answers

What does the variable $v_{obs}(x, y)$ represent in the context of a star or gas cloud's velocity?

<p>Observed radial velocity (A)</p> Signup and view all the answers

A flat rotation curve indicates that $v(r)$ is variable and changes with radius R.

<p>False (B)</p> Signup and view all the answers

What is the unit of measurement for Star Formation Rate (SFR)?

<p>[M⊙ / yr]</p> Signup and view all the answers

The h3 parameter measures the _______ of the Line Of Sight Velocities Distribution.

<p>skewness</p> Signup and view all the answers

Match the types of galaxies with their characteristics:

<p>Fast rotators = Flattened shape, disk-like rotation Slow rotators = Puffy, more spherical shape Rotational support = Rotation supported galaxies Random motion support = Non-rotating galaxies</p> Signup and view all the answers

In a rotating disc, which moment parameter is expected to have an anticorrelation with velocity?

<p>h3 (C)</p> Signup and view all the answers

The third moment h3 and the fourth moment h4 provide insights into the shape of the velocity distribution.

<p>True (A)</p> Signup and view all the answers

What type of galaxies are typically classified as fast rotators?

<p>S0, flat E, spiral galaxies</p> Signup and view all the answers

What describes a galaxy with a constant star formation history (SFH)?

<p>ψ(t) = const. (B)</p> Signup and view all the answers

The fossil approach studies star formation history in galaxies at different redshift.

<p>False (B)</p> Signup and view all the answers

What is the primary characteristic of a single stellar population (SSP)?

<p>A single, infinitesimal burst of star formation.</p> Signup and view all the answers

The _____ elements are produced in Type II supernovae in timescales less than 0.1 [Gyr].

<p>α</p> Signup and view all the answers

Match each type of age/metallicity with its description:

<p>Mean luminosity-weighed age and metallicity (MLW) = Dominated by young and bright stars Mass mean-weighed age and metallicity (MMW) = Dominated by old and heavy stars α-enhancement = Relative abundance ratio of α-elements to Fe</p> Signup and view all the answers

Which of the following is true regarding spectral energy distribution (SED)?

<p>SED is the emission of a galaxy across the entire spectro-magnetic spectrum. (C)</p> Signup and view all the answers

Fe is produced in Type II supernovae with a typical timescale of 1 [Gyr].

<p>False (B)</p> Signup and view all the answers

What can the relative abundance of different metals in a galaxy indicate?

<p>The star formation rate (SFR) of the galaxy.</p> Signup and view all the answers

Flashcards

Milky Way galaxy

The Milky Way is a spiral galaxy containing billions of stars, a central black hole, gas, dust and a dark matter halo. Its total mass is estimated to be approximately 1.16 x 10^12 solar masses.

MBH

The Milky Way's central black hole, with a mass of about 4 million solar masses.

Rsun

The distance from the Sun to the Milky Way's center is approximately 8 kiloparsecs.

tsun-orb

The time it takes for the Sun to complete one orbit around the Milky Way's center is about 250 million years.

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Hubble Constant (H0)

The Hubble constant is a fundamental value in cosmology, representing the rate of expansion of the universe. Its current value is 67.66 ± 0.42 kilometers per second per megaparsec.

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Photometry

A technique for measuring the intensity of radiation from astronomical objects across a wide range of wavelengths.

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Optical Window & Radio Window

The two regions of the electromagnetic spectrum that are visible from Earth's surface.

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Galaxy clusters

These are gravitationally bound collections of galaxies, containing over 100 galaxies in a region with a diameter of a few megaparsecs, and masses of around 10^15 solar masses.

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Bolometric Luminosity (Lbol)

The total energy radiated by an astronomical object across all wavelengths. It's like the 'total light output' of an object.

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Luminosity Density (Lλ)

The energy radiated per unit time per unit wavelength by an astronomical object. It tells you how much light is emitted at specific wavelengths.

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Flux (F)

The energy received per unit time per unit area from a distant astronomical object. It's what we actually measure on Earth.

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Intensity or Surface Brightness

The density of flux per unit of solid angle or area of the sky. It's the brightness of a large region, like a galaxy core.

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Magnitude (m)

A system used to measure the brightness of astronomical objects. It's based on a logarithmic scale.

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AB Magnitude

A particular type of magnitude system, where the zero point is defined by a flux of 3631 Jansky.

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Hubble Sequence

A visual classification scheme for galaxies based on their appearance, focusing on features like shape, bulge prominence, and arm structure.

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CAS Classification

A classification scheme for galaxies that uses the relative prominence of different galaxy components, like bulges and disks, independent of visual appearance.

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Exponential Function

An exponential profile where the intensity decreases exponentially with radius. Used to model disks.

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Sersic Profile

A flexible model used to represent the surface brightness of elliptical galaxies and bulges. It allows for different shapes based on the Sersic index 'n'.

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Ferrers Profile

A profile that describes the projected surface density of a 3D Ferrers ellipsoid. Commonly used to model the surface brightness of bar components in galaxies.

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Type I Disk

A type of galaxy disk where the surface brightness follows a single exponential profile across its entire extent.

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Type II Disk

A galaxy disk with a double exponential law where the surface brightness declines more steeply beyond a specific radius (break radius).

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Type III Disk

A galaxy disk that exhibits an increase in surface brightness in its outer regions. This is a less common type of disk.

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H I Line (21 cm line)

A spectral line emitted by neutral hydrogen atoms. This line is a key tracer of gas distribution and kinematics in galaxies.

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CO Molecular Gas

A molecule used to trace the distribution of molecular gas in galaxies. It's a common molecule in molecular clouds, making it a good proxy for H2.

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Star Formation History (SFH)

A measure of the rate at which stars form in a galaxy over its entire lifetime, often expressed as a function of time.

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Constant SFH

A constant rate of star formation in a galaxy throughout its lifetime. Common in disk galaxies.

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Exponential Decline SFH

A star formation rate that declines exponentially over time, common in older galaxies.

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Single Stellar Population (SSP)

An instantaneous burst of star formation, creating a galaxy with stars of similar age.

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Spectral Energy Distribution (SED)

The sum of all emissions from a galaxy across the entire electromagnetic spectrum.

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Mean Luminosity-Weighted Age and Metallicity (MLW)

The age and metallicity of a galaxy, determined by fitting its SED to a theoretical model.

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Mass Mean-Weighted Age and Metallicity (MMW)

Similar to MLW but weighted by stellar mass, giving more weight to older, massive stars.

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Metallicity

The relative abundance of elements heavier than helium, reflecting the history of star formation in a galaxy.

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Radial Velocity, vobs(x,y)

The observed velocity of a star or gas cloud at a specific radial position and angle within a galaxy, considering galactic inclination.

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Solid Body Rotation Curve (Constant Ω)

The constant rotational speed of a solid body, like a bulge or a bar.

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Flat Rotation Curve (v(r)=v0)

A flat rotation curve indicates a constant velocity for all stars, regardless of their distance from the galactic center.

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Peaked Rotation Curve

A peaked rotation curve suggests that the velocity reaches a maximum and then decreases for stars further away from the galactic center.

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Line of Sight Velocities Distribution (LOSVD)

The distribution of velocities of stars along the line of sight in a galaxy. Commonly modeled using a Gaussian function.

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h3 parameter (Skewness)

A measure of the asymmetry of the LOSVD. A positive h3 indicates a skewed distribution towards higher velocities.

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h4 parameter (Kurtosis)

A measure of the sharpness of the peak in the LOSVD. A high h4 indicates a very sharp peak.

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Specific Angular Momentum

The property of galaxies that can classify them as either rapidly rotating (disk-like) or slowly rotating (spherical).

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H2 Emission

A type of electromagnetic radiation with a wavelength of 2.6 mm, used to observe cold interstellar clouds.

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HII Regions

Regions in space where neutral hydrogen is ionized by ultraviolet (UV) photons from young stars, causing them to emit light at a specific wavelength of 6565 Ã….

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Absorption Stellar Lines

Absorption lines in the spectra of stars caused by the absorption of photons by atoms in the stellar atmospheres.

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Doppler Spectroscopy

A technique used to measure the velocity of objects in space by observing the Doppler shift of spectral lines.

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Datacube

A three-dimensional data cube constructed from spectral data, capturing both spatial information and spectral information.

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Systemic Velocity

The velocity of an object relative to a stationary observer, often measured using Doppler spectroscopy.

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Peculiar Velocity

The velocity of a galaxy after subtracting the effects of the Earth's motion, the Milky Way's motion, and the motion of the solar system.

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Velocity Field

A field showing the velocity of different parts of a galaxy, often derived from Doppler spectroscopy of multiple regions.

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Study Notes

Galactic Observations

  • The Milky Way contains approximately 1011 stars and has a mass of roughly 5 x 1010 solar masses.
  • The central black hole has a mass of about 4 x 106 solar masses.
  • The disk of the Milky Way has a radius of approximately 10 kiloparsecs.
  • The mass of the gas and dust in the Milky Way is estimated at 10% of the total mass.
  • The dark matter halo has a radius of about 200 kiloparsecs and a mass of approximately 1012 solar masses.
  • The typical speed of stars orbiting the galactic center is around 200 kilometers per second.
  • The orbital period of the Sun around the galactic center is about 250 million years.
  • The total mass of the Milky Way is roughly 1.16 x 1012 solar masses.
  • Stars make up about 4.3% of the total mass
  • The central black hole accounts for approximately 0.0003% of the total mass.
  • Gas and dust make up approximately 9.9% of the total mass.
  • Dark matter makes up about 85.8% of the total mass.

Nearby Galaxies

  • Sagittarius dwarf galaxy is located approximately 24 kiloparsecs away.
  • The Large Magellanic Cloud (LMC) is located between 45 and 50 kiloparsecs away and has a luminosity roughly 1010 times the Sun.
  • The Andromeda Galaxy (M31) is roughly 780 kiloparsecs away and has a luminosity of approximately 4 x 1010 the Sun's luminosity.

Galaxy Clusters

  • Galaxy clusters contain more than 100 galaxies.
  • The diameter of galaxy clusters can range from 1 to 5 kiloparsecs.
  • Their masses are greater than 1015 solar masses.
  • The Virgo cluster is one of the closest galaxy clusters, located about 17 megaparsecs away.
  • The Coma cluster is a somewhat more distant cluster, roughly 90 megaparsecs away.

Relative Velocity Between Galaxies

  • The relative velocity (v) between two galaxies at a distance (d) is related to the Hubble constant (Ho) and is determined by the formula: v = Ho x d

Photometry

  • Photometry is used to measure the intensity of radiation from astronomical objects across a broad spectrum of wavelengths.
  • The atmosphere has regions (windows) that allow observation of some wavelengths of light.
  • The atmosphere blocks many wavelengths because of absorption.
  • The luminosity (L) of an object is the energy radiated per unit time, measured in [erg/s]. This is integrated over all wavelengths.
  • Luminosity density (Lx) describes the luminosity of an object in a specific range of wavelengths [erg/s/Ã…].
  • Bolometric luminosity is the total energy radiated across the full spectrum of light.
  • Flux (F) is the energy radiated per unit area per unit time, often reported in units of [erg/s/cm²].
  • The intensity or surface brightness is the measure of flux per unit solid angle.

Photometric Decomposition

  • Photometric decomposition is a technique used to analyze the surface brightness distribution of galaxies.
  • This method involves measuring the intensity of light (I(r)) across the galaxy using isophotes (regions of constant brightness).
  • This information is then plotted on a magnitude scale (μ(r)).
  • Analyzing the PSF (point spread function) helps to model and analyze the blurring effect.
  • Functions like exponential functions and Sersic profiles are used to model galaxy profiles.

Galaxy Kinematics

  • The 21cm Hydrogen line and CO emission lines are used to study galaxy kinematics.
  • The ionized gas (Hα) and absorption lines can also provide insights into galaxy kinematics.

Galaxy Morphological Classification

  • Galaxies are classified based on their visual appearance.
  • Hubble's classification scheme is commonly used, focusing on the visual shape, concentration of light, and the presence of a bar.
  • CAS (Concentration, Asymmetry, Smoothness) classification is another system that is more analytic.

Star Formation Rate (SFR)

  • SFR describes the current rate of star formation in a galaxy.
  • Measured in units of solar masses per year ([M☉/yr]).
  • Tracers include UV continuum, Hα, and other emission lines.

Star Formation History (SFH)

  • SFH describes the star formation rate over the entire lifetime of a galaxy.
  • It can be constant over time, decline exponentially, or have various other patterns.

Single Stellar Populations (SSPs)

  • SSPs represent a single, instantaneous burst of star formation.
  • They are used as a building block to model more complex stellar populations.

Spectral Energy Distribution (SED)

  • SED is a plot of the galaxy's emission across different wavelengths of the electromagnetic spectrum.

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Description

This quiz tests your knowledge on various galactic profiles, including the Sersic profile and its parameters. It also covers important astrophysical measurements and characteristics of our Milky Way galaxy. Challenge yourself with questions about dark matter and the Hubble constant!

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