What is the Sloan Digital Sky Survey? Simply put, the Sloan Digital Sky Survey is the most ambitious...
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What is the Sloan Digital Sky Survey?
Simply put, the Sloan Digital Sky Survey is the most ambitious astronomical survey project ever undertaken. The survey will map in detail one-quarter of the entire sky, determining the positions and absolute brightnesses of more than 100 million celestial objects. It will also measure the distances to more than a million galaxies and quasars. Apache Point Observatory, site of the SDSS telescopes, is operated by the Astrophysical Research Consortium (ARC).
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SDSS DR1
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Función de Luminosidad
Es el numero de Galaxias por unidad de volumen en función de su luminosidad.
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Funcion de luminosidadEn un intento por encontrar un ajuste analítico para las funciones de luminosidad, Paul Schecter propuso la forma funcional:
que también puede ser escrita como:
En ambas formas y L* (o M*) son parámetros libres que son usados para obtener el mejor ajuste posible.
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*** *
)(L
Lde
L
LdLL LL
Notar de la forma que:Notar de la forma que:
-Para galaxias débiles con -Para galaxias débiles con L L L L**, , término término exponencial exponencial
ee-L/L*-L/L* 1 1 y la función tiende a una ley de potencia y la función tiende a una ley de potencia con pendiente con pendiente ..
-En extremo brillante, -En extremo brillante, L > LL > L**, , el término el término exponencial domina, y el número de galaxias exponencial domina, y el número de galaxias rápidamente cae a cerorápidamente cae a cero
-La variable -La variable ** normaliza la función y define la normaliza la función y define la densidad total de galaxias en el universo.densidad total de galaxias en el universo.
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• L * e s l a l u m i n o s i d a d a b s o l u t a d e u n a g a l a x i a b r i l l a n t e e n e l p u n t o d e l q u i e b r e d e l a e x p o n e n c i a l . E n m a g n i t u d e s , M * .
V a l o r e s t í p i c o s d e l a f u n c i ó n d e S c h e c h t e r s o n :
, M * * 0 . 0 0 2 g a l a x i a s p o r M p c 3
D e a c u e r d o a e s t a f u n c i ó n , e l n ú m e r o d e g a l a x i a s e s i n f i n i t o , s i n e m b a r g o , l a l u m i n o s i d a d t o t a l e s f i n i t a .
*** *
)(L
Lde
L
LdLL LL
0
****
*
0
)2()(*
LL
Lde
L
LdLL LL
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)(4.0
1*
*
10
donde
921.0)(
MM
X
X
dMeXdMM
La función de Schechter en magnitudes es:
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Función de luminosidad para dos muestras de galaxias en ambientes diferentes: panel superior, el campo y panel inferior, el Cúmulo de galaxias Virgo (Binggeli et al. 1988, ARA&A, 26, 509)
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COSMOLOGIA 4:
Funcion de luminosidad SDSS
4) Calcularse la funcion de luminosidad de galaxias en el SDSS. a) Familiarizarse con el concepto de funcion de luminosidad y su estimacion, Familiarizarse con los datos de SDSS: Sloan Digital Sky Survey Data Release 1b) Seleccionar una muestra completa y lo mas profunda posible de galaxias con redshifts.c) Crear diferentes sub-catalogos limitados en volumen y luminosidad, y calcular la funcion de luminosidad a trozos, en estos sub-catalogos. Dar una interpretacion fisica de los resultados y su utilidad.d) Comparar el resultado con los resultados publicados por el SDSS con el "commissioning data": http://xxx.arxiv.org/abs/astro-ph/0012085 y con los resultados del 2dFGRS : http://xxx.arxiv.org/abs/astro-ph/01111011
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Motivaciones
Es una característica fundamental de las poblaciones de Galaxias.
Permite corroborar las teorías de evolución estelar a redshifts altos
.
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Problemas
Galaxias lejanas menos brillantes no son discernibles
Hace falta evaluar la distancia de las galaxias
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<Z> = 0.3
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<Z> = 0